Remove redundant QueryLimiting.enable_whitelist?

The `.enable?` and `.enable_whitelist?` methods were originally
logically different cca61980 but converged in 04b64288.

This removes `.enable_whitelist?`.

lib/gitlab/query_limiting.rb

@@ -4,9 +4,8 @@ module Gitlab
   module QueryLimiting
     # Returns true if we should enable tracking of query counts.
     #
-    # This is only enabled in production/staging if we're running on GitLab.com.
-    # This ensures we don't produce any errors that users can't do anything
-    # about themselves.
+    # This is only enabled in development and test to ensure we don't produce
+    # any errors that users of other environments can't do anything about themselves.
     def self.enable?
       Rails.env.development? || Rails.env.test?
     end
@@ -19,7 +18,7 @@ module Gitlab
     # The issue URL is only meant to push developers into creating an issue
     # instead of blindly whitelisting offending blocks of code.
     def self.whitelist(issue_url)
-      return unless enable_whitelist?
+      return unless enable?
 
       unless issue_url.start_with?('https://')
         raise(
@@ -30,9 +29,5 @@ module Gitlab
 
       Transaction&.current&.whitelisted = true
     end
-
-    def self.enable_whitelist?
-      Rails.env.development? || Rails.env.test?
-    end
   end
 end

spec/lib/gitlab/query_limiting_spec.rb

@@ -63,6 +63,20 @@ RSpec.describe Gitlab::QueryLimiting do
 
         expect(transaction.count).to eq(before)
       end
+
+      it 'whitelists when enabled' do
+        described_class.whitelist('https://example.com')
+
+        expect(transaction.whitelisted).to eq(true)
+      end
+
+      it 'does not whitelist when disabled' do
+        allow(described_class).to receive(:enable?).and_return(false)
+
+        described_class.whitelist('https://example.com')
+
+        expect(transaction.whitelisted).to eq(false)
+      end
     end
   end
 end