hiddenapi: Convert API lists to a flags CSV file

Access flags for hiddenapi have been managed as a series of test files,
one file per flag. This requries too many changes every time a flag is
changed or a new flag is introduced. Change `hiddenapi` and `veridex`
to expect flags as a CSV file in the format:

  <api signature>,<flag1>,...,<flagN>

Test: m, phone boots
Test: m test-art
Test: m appcompat
Change-Id: Iffa64b36ffc5524779d5f57c3c6f0c0e84bfc606