recovery_utils: remove FDE support

Support for FDE is being removed from Android, having been replaced by
FBE.  This CL removes the FDE-specific code from recovery_utils:

- Remove the code that wiped FstabEntry::key_loc if it is a block
  device, since key_loc was only used by FDE.

- Remove support for reserving a crypto footer when formatting volumes,
  since crypto footers were only used by FDE.

Bug: 191796797
Change-Id: I90b1e4cacd2f3e5cce77a82a0af744fcc7da9400