lib/crc16: unexport crc16_table and crc16_byte()

Now that neither crc16_table nor crc16_byte() is used outside
lib/crc16.c, fold them into lib/crc16.c.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250513022115.39109-3-ebiggers@kernel.org


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