[BUGFIX] Filtering extensions on remote repository does not respect repository selection

When searching for an extension in the remote repository with the "filter" text field, the currently selected repository is not taken into account and results from the main typo3 repository are returned.

Reason: the repository was still hardcoded to main repository

Change-Id: Ife22540867b58beab0bd7fd882b8a2ea9c02a624
Resolves: #25390
Reviewed-on: http://review.typo3.org/1315
Reviewed-by: Steffen Kamper
Tested-by: Steffen Kamper