Revert "Add option for switching between UMS and MTP/PTP mode. (2/2)"

This reverts commit 5b2afbc16b91217f6350c0b546871d598c4dfbb3.

Conflicts:
	res/values/strings.xml

Change-Id: Ibab78c6e7b264a0055e6295bcba7093f43d1e91c