[BUGFIX] Remove obsolete flushByTags() from wincache

Method flushByTags() was removed from the cache backend interface
since core version 4.6 and fully removed in 6.0. The wincache
backend still implements this method, but it is never used
anywhere, so it can be removed.

Change-Id: I038f1839f77b33173122bb8a0485dd005ee8a5a4
Fixes: #44937
Related: #35818
Releases: 6.1, 6.0
Reviewed-on: https://review.typo3.org/17810
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn