[TASK] Deprecate unused methods in ElementBrowser

There are 3 methods in ElementBrowser which are never used in the core.
We deprecate them, so they can be removed two versions later.

The methods are:
 * checkFolder
 * isWebFolder
 * setRecordList

Releases: 6.2
Resolves: #55985
Change-Id: I3e4f34e7ebaba9e8eeb0332e9f43c0e4acd2e706
Reviewed-on: https://review.typo3.org/27847
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Oliver Klee
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters