Revert "bullhead: Enable MTP over functionfs"

This reverts commit ace8ef676798ad4063103429b637aa5df52353bf.

3.10 kernel is too old to use functionfs with osdescs. We need
to revert to f_mtp to get os_desc functionality.

Test: Use bullhead mtp, sniff for os descs
Bug: 64790536
Change-Id: I81e2227c68384879ef73e1712180ac725e27e6c9
1 file changed