fscrypt: Drop obsolete recommendation to enable optimized SHA-512

Since the crypto kconfig options are being fixed to enable optimized
SHA-512 automatically
(https://lore.kernel.org/linux-crypto/20250616014019.415791-1-ebiggers@kernel.org/),
it is no longer necessary to give a recommendation to enable it.

Link: https://lore.kernel.org/r/20250619193149.138315-1-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@kernel.org>