Move fs_config_[files|dirs]_<partition> to soong

Note that not all partitions are moved to Soong. Soong doesn't yet
support *_dlkm partitions and the oem partition.

This change also removes dead code for support VNDK snapshot.

Finally, as a minor clean up, the leading '_' is dropped from the module
names _fs_config_*. There's no need to hide the module names.

Bug: 337993745
Test: m
Change-Id: I5beec5c6734291b9361f870fc1a8dba19def062e