libafscp: Use strdup, rather than rolling our own

libafscp: Use strdup, rather than rolling our own

   A = malloc(strlen(B)+ 1);
   memset(A, 0, strlen(B) + 1);
   strlcpy(A, B, strlen(B) + 1);
can be more simply written as
   A = strdup(B);

Doing so also avoids a warning from clang that strlcpy isn't checking
for A overflowing.

Change-Id: I0e21f86eda7bdc0ce869e651c5ceb23d7494e1e2
Reviewed-on: http://gerrit.openafs.org/7077
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>