Small refactoring on clear_transaction_record_state

Make sure when we clean the `@_start_transaction_state` var we do it in
the same code-path.
Also this makes `clear_transaction_record_state`, more consistent with `restore_transaction_record_state`

activerecord/lib/active_record/transactions.rb

@@ -295,7 +295,7 @@ def rollback_active_record_state!
     def committed! #:nodoc:
       run_callbacks :commit if destroyed? || persisted?
     ensure
-      @_start_transaction_state.clear
+      clear_transaction_record_state(true)
     end
 
     # Call the +after_rollback+ callbacks. The +force_restore_state+ argument indicates if the record
@@ -353,9 +353,11 @@ def remember_transaction_record_state #:nodoc:
     end
 
     # Clear the new record state and id of a record.
-    def clear_transaction_record_state #:nodoc:
+    def clear_transaction_record_state(force = false) #:nodoc:
       @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
-      @_start_transaction_state.clear if @_start_transaction_state[:level] < 1
+      if force || @_start_transaction_state[:level] < 1
+        @_start_transaction_state.clear
+      end
     end
 
     # Restore the new record state and id of a record that was previously saved by a call to save_record_state.