lib/crc: remove unnecessary prompt for CONFIG_CRC64

All modules that need CONFIG_CRC64 already select it, so there is no
need to bother users about the option.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250304230712.167600-6-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@google.com>