Use fs_config_generator.py to generate fs_config_files/dirs directly

We want to remove target specific host tools and since
fs_config_generate is compiled with a target specific header file, we
instead remove fs_config_generate entirely and allow python to build
the fs_config_files/dirs files directly from config.fs files and
parsed C headers.

Test: associated unit tests and new end to end test
Test: aosp_sailfish, aosp_crosshatch build produces valid fs_config files
Test: aosp_cf_x86_phone build correctly produces empty fs_config files
Change-Id: Idbc63ff56c0979e1e4c17721371de9d9d02dc8ff