SystemUI: Trim whitespace on a string resource

The floating_mode_blacklisted_app string resource has seemingly
unnecessary whitespace. This commit removes that.

Change-Id: I8f24778395912a684e99d9e847d544db9335b114
Merge remote-tracking branch 'pa_upstream/kitkat' into LG
Merge remote-tracking branch 'upstream/kitkat' into kitkat