Revert "Allow to show USB notification"

This reverts commit 611fb8957d7d3ab26036c1cbce9247c112004c47.
Show USB notification if persist.sys.usb.config is set to mtp,adb

This enable http://review.cyanogenmod.org/#/c/35193/

Change-Id: I5be9452a9e47c7d57c9334aad8149410503bca87