[BUGFIX][Cache] Typo3DbBackend forgets tag entries in flushByTag

flushByTags removes cache entries tagged with a given tag, but
if those cache entries have other tags assigned, they are not
deleted in the tags table.
The patch fixes this with an additional query.

Resolves: #48984
Releases: 6.2, 6.1, 6.0
Change-Id: I7096e63cf823633f0c8a47f698bd475d7d02b83c
Reviewed-on: https://review.typo3.org/21309
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters