Revert "Track our own Nexus 7 (2013) kernel"

This reverts commit efafbaf15d70c7c45ebe76484160a95a5b93b65b.
Revert "Track our ASUS vendor"

This reverts commit ca6a830c70915027b8919c7f2f83054995c13114.
Revert "Track our own Nexus 7 (2013) trees"

This reverts commit 65bfc13c9dd514d541b5b618e0358a77784a8f66.

Change-Id: I4247144f6452b4b2c9351554a90c29691b29c96a
Track our Qualcomm keymaster repo