[ticket/11713] Do not remove module if it couldn't be deleted

Up to now, the module or module category was always removed with jQuery,
even if there was an error. With this change, the modules will not be deleted
by jQuery if the return JSON array will have SUCCESS set to false.

PHPBB3-11713
Merge pull request #1584 from marc1706/ticket/11713

[ticket/11713] Do not remove module if it couldn't be deleted