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.

Reviewed-on: http://gerrit.openafs.org/7077
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 1e30c00e7d9b45d65e819d39414939f2d5f7631b)

Change-Id: I886bef77fdedb63d1c83e657c25d112e0a635db2
Reviewed-on: http://gerrit.openafs.org/11844
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>