ART: Simplify patchoat

Removed unused configurations. Cut out cruft that isn't used anymore
since multi-image. Make it smaller to not require new selinux
permissions for OTAs.

Split up the main function, to make the flow clearer for image vs
app/oat.

Bug: 25612095
Bug: 26317072
Change-Id: Ieb55bd1a13cbb44fd0e2979a8a61a509df9c1e7e