[BUGFIX] Fix invalid global for getData hooks

Replace the invalid usage of $TYPO3_CONF_VARS with
$GLOBALS['TYPO3_CONF_VARS'] for getting the hook
configuration in ContentObjectRenderer::getData().

This bug was introduced with issue #50606 in 6.2 only.

Resolves: #50606
Related: #50258
Releases: 6.2
Change-Id: Ib553f8c0dacd891e4bd392481ef7b4773386287f
Reviewed-on: https://review.typo3.org/22735
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn