Remove unused pixelmatch dependency

We recently removed favicon specs from karma, which were the only ones
utilizing the pixelmatch library.

See: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/50530

package.json

@@ -205,7 +205,6 @@
     "mock-apollo-client": "^0.5.0",
     "node-sass": "^4.14.1",
     "nodemon": "^2.0.4",
-    "pixelmatch": "^4.0.2",
     "postcss": "^7.0.14",
     "prettier": "2.2.1",
     "readdir-enhanced": "^2.2.4",

spec/javascripts/matchers.js

-import pixelmatch from 'pixelmatch';
-
-export default {
-  toImageDiffEqual: () => {
-    const getImageData = (img) => {
-      const canvas = document.createElement('canvas');
-      canvas.width = img.width;
-      canvas.height = img.height;
-      canvas.getContext('2d').drawImage(img, 0, 0);
-      return canvas.getContext('2d').getImageData(0, 0, img.width, img.height).data;
-    };
-
-    return {
-      compare(actual, expected, threshold = 0.1) {
-        if (actual.height !== expected.height || actual.width !== expected.width) {
-          return {
-            pass: false,
-            message: `Expected image dimensions (h x w) of ${expected.height}x${expected.width}.
-            Received an image with ${actual.height}x${actual.width}`,
-          };
-        }
-
-        const { width, height } = actual;
-        const differentPixels = pixelmatch(
-          getImageData(actual),
-          getImageData(expected),
-          null,
-          width,
-          height,
-          { threshold },
-        );
-
-        return {
-          pass: differentPixels < 20,
-          message: `${differentPixels} pixels differ more than ${
-            threshold * 100
-          } percent between input and output.`,
-        };
-      },
-    };
-  },
-};

spec/javascripts/test_bundle.js

@@ -12,7 +12,6 @@ import Vue from 'vue';
 import { getDefaultAdapter } from '~/lib/utils/axios_utils';
 import Translate from '~/vue_shared/translate';
 
-import customMatchers from './matchers';
 import { FIXTURES_PATH, TEST_HOST } from './test_constants';
 
 // Tech debt issue TBD
@@ -57,7 +56,6 @@ beforeAll(() => {
       inline: window.__karma__.config.color,
     }),
   );
-  jasmine.addMatchers(customMatchers);
 });
 
 // globalize common libraries

yarn.lock

@@ -9346,13 +9346,6 @@ pirates@^4.0.1:
   dependencies:
     node-modules-regexp "^1.0.0"
 
-pixelmatch@^4.0.2:
-  version "4.0.2"
-  resolved "https://registry.yarnpkg.com/pixelmatch/-/pixelmatch-4.0.2.tgz#8f47dcec5011b477b67db03c243bc1f3085e8854"
-  integrity sha1-j0fc7FARtHe2fbA8JDvB8wheiFQ=
-  dependencies:
-    pngjs "^3.0.0"
-
 pkg-dir@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/pkg-dir/-/pkg-dir-2.0.0.tgz#f6d5d1109e19d63edf428e0bd57e12777615334b"
@@ -9374,11 +9367,6 @@ pkg-dir@^4.1.0, pkg-dir@^4.2.0:
   dependencies:
     find-up "^4.0.0"
 
-pngjs@^3.0.0:
-  version "3.3.3"
-  resolved "https://registry.yarnpkg.com/pngjs/-/pngjs-3.3.3.tgz#85173703bde3edac8998757b96e5821d0966a21b"
-  integrity sha512-1n3Z4p3IOxArEs1VRXnZ/RXdfEniAUS9jb68g58FIXMNkPJeZd+Qh4Uq7/e0LVxAQGos1eIUrqrt4FpjdnEd+Q==
-
 pofile@1.0.x:
   version "1.0.11"
   resolved "https://registry.yarnpkg.com/pofile/-/pofile-1.0.11.tgz#35aff58c17491d127a07336d5522ebc9df57c954"