[!!!][TASK] Remove ExtJS Pagetree indicator functionality

The ExtJS Page Tree has some functionality to add custom indicators
to the page tree, which is loaded by ExtDirect.

If you wonder what an indicator is, it's the blue box (or some
other HTML content) which is shown if a temporary mount is
shown or if a filter is active.

However, both temporary mount points and filter information
messages are custom, and not handled via the Page Tree.

The functionality is hidden, and was never documented,
and no public extension used this code (not even google found
something).

Therefore I opt to remove it without substitution.

Resolves: #79228
Releases: master
Change-Id: I4097cd3fbbdf736cc2a09e8258199b5aac01a1bc
Reviewed-on: https://review.typo3.org/51228


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>