Remove includes of non-standard alloca.h header.

The alloca.h header is not present on FreeBSD, even though alloca() is
available. Including stdlib.h should be enough on all platforms that
support alloca().

common/netjack_packet.c

@@ -39,7 +39,6 @@
 #define _GNU_SOURCE
 #endif
 
-#include <alloca.h>
 #include <math.h>
 #include <stdio.h>
 #include <memory.h>

tools/alsa_out.c

@@ -4,7 +4,6 @@
  * as they would be used by many applications.
  */
 
-#include <alloca.h>
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>

tools/session_notify.c

@@ -19,7 +19,6 @@
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
-#include <alloca.h>
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>