[BUGFIX] Adjust variable name for install tool password hint

Usage of $TYPO3_CONF_VARS is discouraged, instead
$GLOBALS['TYPO3_CONF_VARS'] should be used. The hint in next to the
install tool login mask spells the discouraged version, which is
corrected with this patch.

Change-Id: Ia7ded107a9b5670c0bc35da92993e84ad45c167e
Releases: master, 6.2
Resolves: #60639
Reviewed-on: http://review.typo3.org/31992
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>