Remove non-updatable-* prefix from .txt files

The services/api/{current,removed,lint-baseline}.txt files used to
contain information for the merged system server stubs. Those files are
now created by the rules in api/Android.bp
('services-system-server-current.txt' and 'services-system-server-removed.txt').

Test: m checkapi
Bug: 177640454
Change-Id: I365be0a45126a6a056d5219e24ef93020c034c87