fscrypto: remove unneeded Kconfig dependencies

SHA256 and ENCRYPTED_KEYS are not needed.  CTR shouldn't be needed
either, but I left it for now because it was intentionally added by
commit 71dea01e ("ext4 crypto: require CONFIG_CRYPTO_CTR if ext4
encryption is enabled").  So it sounds like there may be a dependency
problem elsewhere, which I have not been able to identify specifically,
that must be solved before CTR can be removed.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>