Binder: don't call getCallingUid for RPC calls

All the code using getCallingUid here should be
ripped out anyway because it's Java-centric. Here
are some of the issues with the current stuff around
here:
- it's broken because it won't handle things happening in
  native code
- it's slow (e.g. big transactions are already logged in
  native code anyway)

Bug: 254835230
Test: boots, atest MicrodroidTestApp (with new tests)
Change-Id: I7315059bff138966e9509f1d529a6417466d2b7f