[BUGFIX] Show error message when hiding page from context menu

Renamed key in the response to match what is expected
in actions.js evaluateResponse method.

Releases: 8.7, 7.6
Resolves: #82282
Change-Id: I4528963aded3a8203ab144c8353fc0509aa8a1e7
Reviewed-on: https://review.typo3.org/55905


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>