Don't drop internal metadata tables

Some tests expects that internal metadata tables exists, and we should
not use `create_table` in transactional tests, since DDL in MySQL causes
implicit commit.

https://travis-ci.org/rails/rails/jobs/515438937#L3829

activerecord/test/cases/tasks/database_tasks_test.rb

@@ -50,7 +50,6 @@ def test_raises_an_error_when_called_with_protected_environment
       protected_environments = ActiveRecord::Base.protected_environments
       current_env            = ActiveRecord::Base.connection.migration_context.current_environment
 
-      InternalMetadata.create_table
       InternalMetadata[:environment] = current_env
 
       assert_called_on_instance_of(
@@ -77,7 +76,6 @@ def test_raises_an_error_when_called_with_protected_environment_which_name_is_a_
       protected_environments = ActiveRecord::Base.protected_environments
       current_env            = ActiveRecord::Base.connection.migration_context.current_environment
 
-      InternalMetadata.create_table
       InternalMetadata[:environment] = current_env
 
       assert_called_on_instance_of(
@@ -966,8 +964,8 @@ def setup
       end
 
       def teardown
-        SchemaMigration.drop_table
-        InternalMetadata.drop_table
+        SchemaMigration.delete_all
+        InternalMetadata.delete_all
         ActiveRecord::Base.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
       end