[DAC FIXIT]: Noted that UNINSTALL_SHORTCUT is no longer supported.

Per b/25487830, this permission is no longer supported. I don't think
I can remove it from the manifest file, so unless someone has a better
idea, I'm just replacing the existing doc with a comment saying that
it's not supported.

Doc is staged to:
http://go/dac-stage/reference/android/Manifest.permission.html#UNINSTALL_SHORTCUT

bug: 25487830
Change-Id: Ib564fb49536626df6f92bd2b97a11ffec41e9a90