arch, net: remove the last csum_partial_copy() leftovers

Most of the tree only uses and implements csum_partial_copy_nocheck,
but the c6x and lib/checksum.c implement a csum_partial_copy that
isn't used anywere except to define csum_partial_copy.  Get rid of
this pointless alias.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>