[BUGFIX] Constant styles.content.imgtext.responsive is not used

Removed the entry from constants.txt

Resolves: #52998
Releases: 6.2
Change-Id: I896bc6113ff4dd6015fecaf2f80d573aeab8a02f
Reviewed-on: https://review.typo3.org/24918
Reviewed-by: Sebastian Fischer
Tested-by: Sebastian Fischer
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters