[TASK] Deprecate 'path' of extra click menu option registration

Deprecate option 'path' aption of the extendCMclasses registration
array, the autoloader should take care of finding and loading those.

Change-Id: Ibb3edcf3e87a0384f566be8dcdfa016b3731f943
Resolves: #45098
Releases: 6.1
Reviewed-on: https://review.typo3.org/17965
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn