Remove obsolete droidstub args

- I see no usages of private_api_filename / private.txt /
  private_dex_api_filename
- tags are no longer used as of
  Iff355041d88eb59ac47dd19a03e993cf1ce3927e
- api_filename/removed_api_filename does nothing if check_api is
  specified. test-api does not need a removed.txt

Bug: 152479829
Bug: 144149403
Test: m
Change-Id: Ic1e859dc6aa91f8d7b4f285b63d3faafb27edc9b