chan_iax2: System Header strings is included via asterisk.h/compat.h.

The system header strings was included mistakenly with commit 3de0204.
That header is included via asterisk.h and there via the compat.h.

Change-Id: I3dc49060e275295f785670c87cc65fd3c3abd24a

channels/chan_iax2.c

@@ -68,7 +68,6 @@
 #include <netinet/ip.h>
 #include <sys/time.h>
 #include <signal.h>
-#include <strings.h>
 #include <netdb.h>
 #include <fcntl.h>
 #include <sys/stat.h>