Remove omniauth_initializer_fullhost_proc FF

This has been enabled by default in 15.0, this is cleaning
up the remaining FF logic.

Changelog: other

config/feature_flags/development/omniauth_initializer_fullhost_proc.yml

----
-name: omniauth_initializer_fullhost_proc
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82703
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/355579
-milestone: '14.10'
-type: development
-group: group::geo
-default_enabled: true

config/initializers/omniauth.rb

@@ -11,14 +11,7 @@ module OmniAuth::Strategies
   end
 end
 
-OmniAuth.config.full_host =
-  if Feature.feature_flags_available? && ::Feature.enabled?(:omniauth_initializer_fullhost_proc)
-    Gitlab::AppLogger.debug("Using OmniAuth proc initializer")
-    Gitlab::OmniauthInitializer.full_host
-  else
-    Gitlab::AppLogger.debug("Fallback to OmniAuth static full_host")
-    Settings.gitlab['base_url']
-  end
+OmniAuth.config.full_host = Gitlab::OmniauthInitializer.full_host
 
 OmniAuth.config.allowed_request_methods = [:post]
 # In case of auto sign-in, the GET method is used (users don't get to click on a button)

spec/initializers/omniauth_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe 'OmniAuth initializer for GitLab' do
-  let(:load_omniauth_initializer) do
+  def load_omniauth_initializer
     load Rails.root.join('config/initializers/omniauth.rb')
   end
 
@@ -15,32 +15,15 @@
     before do
       allow(Settings).to receive(:gitlab).and_return({ 'base_url' => base_url })
       allow(Gitlab::OmniauthInitializer).to receive(:full_host).and_return('proc')
-    end
-
-    context 'with feature flags not available' do
-      before do
-        expect(Feature).to receive(:feature_flags_available?).and_return(false)
-        load_omniauth_initializer
-      end
 
-      it { is_expected.to eq(base_url) }
+      load_omniauth_initializer
     end
 
-    context 'with the omniauth_initializer_fullhost_proc FF disabled' do
-      before do
-        stub_feature_flags(omniauth_initializer_fullhost_proc: false)
-        load_omniauth_initializer
-      end
-
-      it { is_expected.to eq(base_url) }
+    # to clear existing mocks and prevent order-dependent failures
+    after(:all) do
+      load_omniauth_initializer
     end
 
-    context 'with the omniauth_initializer_fullhost_proc FF disabled' do
-      before do
-        load_omniauth_initializer
-      end
-
-      it { is_expected.to eq('proc') }
-    end
+    it { is_expected.to eq('proc') }
   end
 end