tree-wide: drop alloca.h when alloc-util.h is included

src/shared/calendarspec.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include <alloca.h>
 #include <ctype.h>
 #include <errno.h>
 #include <limits.h>

src/shared/fdset.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include <alloca.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stddef.h>

src/shared/firewall-util.c

@@ -5,7 +5,6 @@
  */
 #define _NET_IF_H 1
 
-#include <alloca.h>
 #include <arpa/inet.h>
 #include <endian.h>
 #include <errno.h>