Remove 'one_megabyte_file_size_limit' feature flag

Changelog: removed

config/feature_flags/development/one_megabyte_file_size_limit.yml

----
-name: one_megabyte_file_size_limit
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/65167
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/334916
-milestone: '14.1'
-type: development
-group: group::code review
-default_enabled: false

lib/gitlab/highlight.rb

@@ -50,11 +50,7 @@ module Gitlab
     attr_reader :context
 
     def self.file_size_limit
-      if Feature.enabled?(:one_megabyte_file_size_limit)
-        1024.kilobytes
-      else
-        Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
-      end
+      Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
     end
 
     private_class_method :file_size_limit

spec/lib/gitlab/highlight_spec.rb

@@ -50,16 +50,9 @@ RSpec.describe Gitlab::Highlight do
       let(:result) { described_class.highlight(file_name, content) } # content is 44 bytes
 
       before do
-        stub_feature_flags(one_megabyte_file_size_limit: false)
         stub_config(extra: { 'maximum_text_highlight_size_kilobytes' => 0.0001 } ) # 1.024 bytes
       end
 
-      it 'confirm file size is 1MB when `one_megabyte_file_size_limit` is enabled' do
-        stub_feature_flags(one_megabyte_file_size_limit: true)
-        expect(described_class.too_large?(1024.kilobytes)).to eq(false)
-        expect(described_class.too_large?(1025.kilobytes)).to eq(true)
-      end
-
       it 'increments the metric for oversized files' do
         expect { result }.to change { over_highlight_size_limit('file size: 0.0001') }.by(1)
       end