Revert "[BUGFIX] Unified maxitems default value for group fields"

Unexpected behaviour. Default of maxitems in now 1 by default
which doesn't work if you need more items. Previously this
was possible. Revert this to have the old working
behaviour again.

Releases: 6.3,6.2
Resolves: #60263
Reverts: #55731
This reverts commit c578d47617f803c9ea167d88000e63a92c13fa93.

Change-Id: Ice5357aecb1969f11c6821cb81824d2d68200717
Reviewed-on: http://review.typo3.org/32284
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>