Remove @utf8 support

The annotation is not used anywhere. We now only support @utf8InCpp
where strings are stored in UTF16 format on the wire but allows it to be
read/written in UTF8 format.

Bug: 117453706
Test: system/tools/aidl/runtests.sh
Change-Id: Ie5b5b3f241f8a7540563e9de1e059156b5922e20
5 files changed