Breaking: #78521 - Drop unused JavaScript from backend.js

See forge#78521

Description

The following JavaScript methods related to ExtJS have been removed from the Backend main frame as defined in the main backend.js file.

TYPO3._instances
TYPO3.addInstance
TYPO3.getInstance
TYPO3.helpers.split

Impact

Any call to one of the above mentioned methods will result in a JavaScript error.

Affected Installations

Any installation that uses one of the methods mentioned above.