Remove unused loading_button component

Since the epic to migrate away from this component
has been complete.
https://gitlab.com/groups/gitlab-org/-/epics/3907

app/assets/javascripts/import_projects/components/import_projects_table.vue

@@ -178,11 +178,7 @@ export default {
       :key="pagePaginationStateKey"
       @appear="fetchRepos"
     />
-    <gl-loading-icon
-      v-if="isLoading"
-      class="js-loading-button-icon import-projects-loading-icon"
-      size="md"
-    />
+    <gl-loading-icon v-if="isLoading" class="import-projects-loading-icon" size="md" />
 
     <div v-if="!isLoading && repositories.length === 0" class="text-center">
       <strong>{{ emptyStateText }}</strong>

app/assets/javascripts/vue_shared/components/loading_button.vue

-<script>
-import { GlLoadingIcon } from '@gitlab/ui';
-/* eslint-disable vue/require-default-prop */
-/*
-This component will be deprecated in favor of gl-deprecated-button.
-https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-button--loading-button
-https://gitlab.com/gitlab-org/gitlab/issues/207412
-*/
-
-export default {
-  components: {
-    GlLoadingIcon,
-  },
-  props: {
-    loading: {
-      type: Boolean,
-      required: false,
-      default: false,
-    },
-    disabled: {
-      type: Boolean,
-      required: false,
-      default: false,
-    },
-    label: {
-      type: String,
-      required: false,
-    },
-    containerClass: {
-      type: [String, Array, Object],
-      required: false,
-      default: 'btn btn-align-content',
-    },
-  },
-  methods: {
-    onClick(e) {
-      this.$emit('click', e);
-    },
-  },
-};
-</script>
-
-<template>
-  <button :class="containerClass" :disabled="loading || disabled" type="button" @click="onClick">
-    <transition name="fade-in">
-      <gl-loading-icon
-        v-if="loading"
-        :inline="true"
-        :class="{
-          'gl-mr-2': label,
-        }"
-        class="js-loading-button-icon"
-      />
-    </transition>
-    <transition name="fade-in">
-      <slot>
-        <span v-if="label" class="js-loading-button-label"> {{ label }} </span>
-      </slot>
-    </transition>
-  </button>
-</template>

spec/frontend/vue_shared/components/loading_button_spec.js

-import { shallowMount } from '@vue/test-utils';
-import LoadingButton from '~/vue_shared/components/loading_button.vue';
-
-const LABEL = 'Hello';
-
-describe('LoadingButton', () => {
-  let wrapper;
-
-  afterEach(() => {
-    wrapper.destroy();
-  });
-
-  const buildWrapper = (propsData = {}) => {
-    wrapper = shallowMount(LoadingButton, {
-      propsData,
-    });
-  };
-  const findButtonLabel = () => wrapper.find('.js-loading-button-label');
-  const findButtonIcon = () => wrapper.find('.js-loading-button-icon');
-
-  describe('loading spinner', () => {
-    it('shown when loading', () => {
-      buildWrapper({ loading: true });
-
-      expect(findButtonIcon().exists()).toBe(true);
-    });
-  });
-
-  describe('disabled state', () => {
-    it('disabled when loading', () => {
-      buildWrapper({ loading: true });
-      expect(wrapper.attributes('disabled')).toBe('disabled');
-    });
-
-    it('not disabled when normal', () => {
-      buildWrapper({ loading: false });
-
-      expect(wrapper.attributes('disabled')).toBe(undefined);
-    });
-  });
-
-  describe('label', () => {
-    it('shown when normal', () => {
-      buildWrapper({ loading: false, label: LABEL });
-      expect(findButtonLabel().text()).toBe(LABEL);
-    });
-
-    it('shown when loading', () => {
-      buildWrapper({ loading: false, label: LABEL });
-      expect(findButtonLabel().text()).toBe(LABEL);
-    });
-  });
-
-  describe('container class', () => {
-    it('should default to btn btn-align-content', () => {
-      buildWrapper();
-
-      expect(wrapper.classes()).toContain('btn');
-      expect(wrapper.classes()).toContain('btn-align-content');
-    });
-
-    it('should be configurable through props', () => {
-      const containerClass = 'test-class';
-
-      buildWrapper({
-        containerClass,
-      });
-
-      expect(wrapper.classes()).not.toContain('btn');
-      expect(wrapper.classes()).not.toContain('btn-align-content');
-      expect(wrapper.classes()).toContain(containerClass);
-    });
-  });
-
-  describe('click callback prop', () => {
-    it('calls given callback when normal', () => {
-      buildWrapper({
-        loading: false,
-      });
-
-      wrapper.trigger('click');
-
-      return wrapper.vm.$nextTick().then(() => {
-        expect(wrapper.emitted('click')).toBeTruthy();
-      });
-    });
-
-    it('does not call given callback when disabled because of loading', () => {
-      buildWrapper({
-        loading: true,
-      });
-
-      wrapper.trigger('click');
-
-      return wrapper.vm.$nextTick().then(() => {
-        expect(wrapper.emitted('click')).toBeFalsy();
-      });
-    });
-  });
-});