Add @UnsupportedAppUsage annotations

For packages:
  android.mtp

This is an automatically generated CL. See go/UnsupportedAppUsage
for more details.

Exempted-From-Owner-Approval: Mechanical changes to the codebase
which have been approved by Android API council and announced on
android-eng@

Bug: 110868826
Test: m
Change-Id: I6af7c9405b0ac3c2d30307dd04d6d330cd22bda4
Merged-In: Id97d70dc1003cd7c6ed585d647bf0df0fd7a946a