Disable CI variable complex expressions by default

lib/gitlab/ci/pipeline/expression/lexeme/matches.rb

@@ -36,7 +36,7 @@ module Gitlab
             private
             def ci_variables_complex_expressions?
-              Feature.enabled?(:ci_variables_complex_expressions, default_enabled: true)
+              Feature.enabled?(:ci_variables_complex_expressions)
             end
           end
         end

lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb

@@ -34,7 +34,7 @@ module Gitlab
             end
             def self.eager_matching_with_escape_characters?
-              Feature.enabled?(:ci_variables_complex_expressions, default_enabled: true)
+              Feature.enabled?(:ci_variables_complex_expressions)
             end
           end
         end

lib/gitlab/ci/pipeline/expression/lexer.rb

@@ -73,7 +73,7 @@ module Gitlab
           end
           def available_lexemes
-            Feature.enabled?(:ci_variables_complex_expressions, default_enabled: true) ? NEW_LEXEMES : LEXEMES
+            Feature.enabled?(:ci_variables_complex_expressions) ? NEW_LEXEMES : LEXEMES
           end
         end
       end

lib/gitlab/ci/pipeline/expression/parser.rb

@@ -13,7 +13,7 @@ module Gitlab
           end
           def tree
-            if Feature.enabled?(:ci_variables_complex_expressions, default_enabled: true)
+            if Feature.enabled?(:ci_variables_complex_expressions)
               rpn_parse_tree
             else
               reverse_descent_parse_tree