tools: mkeficapsule: dont use malloc.h

malloc() functions are declared via stdlib.h. Including  malloc.h can lead
to build errors e.g. on OS-X.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

tools/mkeficapsule.c

@@ -5,7 +5,6 @@
  */
 
 #include <getopt.h>
-#include <malloc.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>