Roll back support for caching encoding detection

This feature can lead to correctness issues with binary detection (see
https://gitlab.com/gitlab-org/gitlab/-/issues/340013) since blob data is
not guaranteed to be loaded entirely when detection is run.

Benchmarks in https://gitlab.com/gitlab-org/gitlab/-/issues/34001 show
on staging that the cost of Redis lookups can be 80x slower than just
running Charlock Holmes of up to 8000 characters per file.

Relates to:

* https://gitlab.com/gitlab-org/gitlab/-/issues/340013
* https://gitlab.com/gitlab-org/gitlab/-/issues/328819

Changelog: changed

config/feature_flags/development/cached_encoding_detection.yml

----
-name: cached_encoding_detection
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60128
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/328819
-milestone: '13.12'
-type: development
-group: group::source code
-default_enabled: false

lib/gitlab/encoding_helper.rb

@@ -40,15 +40,7 @@ module Gitlab
     def detect_encoding(data, limit: CharlockHolmes::EncodingDetector::DEFAULT_BINARY_SCAN_LEN, cache_key: nil)
       return if data.nil?
 
-      if Feature.enabled?(:cached_encoding_detection, type: :development, default_enabled: :yaml)
-        return CharlockHolmes::EncodingDetector.new(limit).detect(data) unless cache_key.present?
-
-        Rails.cache.fetch([:detect_binary, CharlockHolmes::VERSION, cache_key], expires_in: 1.week) do
-          CharlockHolmes::EncodingDetector.new(limit).detect(data)
-        end
-      else
-        CharlockHolmes::EncodingDetector.new(limit).detect(data)
-      end
+      CharlockHolmes::EncodingDetector.new(limit).detect(data)
     end
 
     def detect_binary?(data, detect = nil)

spec/lib/gitlab/encoding_helper_spec.rb

@@ -241,7 +241,7 @@ RSpec.describe Gitlab::EncodingHelper do
     let(:data) { binary_string }
     let(:kwargs) { {} }
 
-    shared_examples 'detects encoding' do
+    context 'detects encoding' do
       it { is_expected.to be_a(Hash) }
 
       it 'correctly detects the binary' do
@@ -264,33 +264,5 @@ RSpec.describe Gitlab::EncodingHelper do
         end
       end
     end
-
-    context 'cached_encoding_detection is enabled' do
-      before do
-        stub_feature_flags(cached_encoding_detection: true)
-      end
-
-      it_behaves_like 'detects encoding'
-
-      context 'cache_key is provided' do
-        let(:kwargs) do
-          { cache_key: %w(foo bar) }
-        end
-
-        it 'uses that cache_key to serve from the cache' do
-          expect(Rails.cache).to receive(:fetch).with([:detect_binary, CharlockHolmes::VERSION, %w(foo bar)], expires_in: 1.week).and_call_original
-
-          expect(subject[:type]).to eq(:binary)
-        end
-      end
-    end
-
-    context 'cached_encoding_detection is disabled' do
-      before do
-        stub_feature_flags(cached_encoding_detection: false)
-      end
-
-      it_behaves_like 'detects encoding'
-    end
   end
 end