Revert "Add ParseFstabFromString(), remove ReadFstabFromFp()"

Revert submission 1890098

Reason for revert: Breaks tests, b/206740783
Reverted Changes:
I71190c735:Add ParseFstabFromString(), remove ReadFstabFromFp...
Ic1dd0eb97:Replace strtok_r() with C++-style android::base::T...

Change-Id: I1ded0217670a9bf3f2485120ee0dddf3e854a6fb
3 files changed