Revert "jessie: Install xbindkeys directly from mirror."

This reverts commit 19c75c0959aeaf6c3a0be6c1ea2f7b3584335c0b.

xbindkeys has been added back in jessie repository:
https://packages.debian.org/search?keywords=xbindkeys
Merge pull request #656 from drinkcat/xbindkeys-jessie-revert

Revert "jessie: Install xbindkeys directly from mirror."
Merge remote-tracking branch 'crouton/master'