[BUGFIX] Only show download location as configured

Extension manager shows possible locations to install an Extension.
The options set in the Install Tool must be shown.

Change-Id: I6d51c1a71eb4ff83077cf3962fadbcefb5049637
Fixes: #42103
Releases: 6.0
Reviewed-on: http://review.typo3.org/15778
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel