libbinder: RPC - remove 'agreed experimental'

Where this can be used is still limited by sepolicy, but now that we
have examples for how to version the wire protocol, tests, fuzzer
entries, and most performance analysis is done, we can avoid this
function name.

Bug: 167966510
Test: N/A
Change-Id: Ibda9a656f1b96be7d38c4684cab787e411297a24