[TASK] Don't set extensions checked by default in InstallSysExtsUpdate

In the InstallSysExtsUpdate update wizard the extensions are checked
by default. This gives the indication that the extensions need
to be installed. In fact they are optional and therefore should
not be checked by default.

Change-Id: Ic61ad081b08d1906d224a29c79702db3fe1597e1
Resolves: #47733
Releas: 6.2
Reviewed-on: https://review.typo3.org/23827
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring