take the dummy csum_and_copy_from_user() into net/checksum.h

now that can be done conveniently - all non-trivial cases have
_HAVE_ARCH_COPY_AND_CSUM_FROM_USER defined, so the fallback in
net/checksum.h is used only for dummy (copy_from_user, then
csum_partial) implementation.  Allowing us to get rid of all
dummy instances, both of csum_and_copy_from_user() and
csum_partial_copy_from_user().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

lib/checksum.c

@@ -145,26 +145,6 @@ __sum16 ip_compute_csum(const void *buff, int len)
 }
 EXPORT_SYMBOL(ip_compute_csum);
 
-/*
- * copy from fs while checksumming, otherwise like csum_partial
- */
-__wsum
-csum_partial_copy_from_user(const void __user *src, void *dst, int len,
-						__wsum sum, int *csum_err)
-{
-	int missing;
-
-	missing = __copy_from_user(dst, src, len);
-	if (missing) {
-		memset(dst + len - missing, 0, missing);
-		*csum_err = -EFAULT;
-	} else
-		*csum_err = 0;
-
-	return csum_partial(dst, len, sum);
-}
-EXPORT_SYMBOL(csum_partial_copy_from_user);
-
 /*
  * copy from ds while checksumming, otherwise like csum_partial
  */