[BUGFIX] Temporary DB tree mount notice missing in ElementBrowser

If "Stop Page Tree" is set for a page, it is possible to set temporary
DB tree mounts in the element browser/link browser.
If such a tree mount is set, a notice is displayed right above the tree.

This notice is necessary to cancel this temporary mount.
Currently the ElementBrowser misses this notice when used
for e.g. header_link.

Change-Id: I942aad0e54d17ceb793008850f0563bb416503be
Fixes: #43885
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/28182
Reviewed-by: Markus Klein
Tested-by: Markus Klein