Revert commit 4ec5b0d6b4 in favor of #28379

Commit 4ec5b0d was for fixing the regression #18787, but #28379 fixes
#18787 as well. So 4ec5b0d is no longer necessary.

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -537,12 +537,7 @@ module ActiveRecord
         end
 
         def extract_limit(sql_type)
-          case sql_type
-          when /^bigint/i
-            8
-          when /\((.*)\)/
-            $1.to_i
-          end
+          $1.to_i if sql_type =~ /\((.*)\)/
         end
 
         def translate_exception_class(e, sql)

activerecord/test/cases/connection_adapters/type_lookup_test.rb

@@ -82,11 +82,11 @@ unless current_adapter?(:PostgreSQLAdapter) # PostgreSQL does not use type strin
         end
 
         def test_bigint_limit
-          cast_type = @connection.send(:type_map).lookup("bigint")
+          limit = @connection.send(:type_map).lookup("bigint").send(:_limit)
           if current_adapter?(:OracleAdapter)
-            assert_equal 19, cast_type.limit
+            assert_equal 19, limit
           else
-            assert_equal 8, cast_type.limit
+            assert_equal 8, limit
           end
         end