Revert "Allow to show USB notification"

This reverts commit 51524bef5de7963e5da68bc8b8311f6c192c68b3.
Show USB notification if persist.sys.usb.config is set to mtp,adb

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

Change-Id: I5be9452a9e47c7d57c9334aad8149410503bca87