remove duplicate loaded personal.js - fixes #12674

fixes #12674

steps to reproduce:

* enable `files_encryption`
* go to personal settings
* verify that `settings/js/personal.js` is loaded twice
* patch it with this changes
* go to personal settings
* verify that `settings/js/personal.js` is loaded once


@DeepDiver1975 Shouldn't that be prevent by the addScript handler that a file is only added once?

cc @PVince81 @LukasReschke @schiesbn @wakeup @chrsch 

This was introduced with https://github.com/owncloud/core/commit/64d94c540aeaba67e2f779b2551c72a80334aa3e#diff-5419adee45fc55a23d91d2dc9ede0fbaR35