Revert "lib: bootm: add missing include"

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This reverts commit 1e96220a56.

Remove duplicated vxworks.h header.
The same change was done by
"ARM: prevent compiler warnings from bootm.c"
(sha1: 8d196e52b5)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/lib/bootm.c

@@ -15,7 +15,6 @@
 #include <common.h>
 #include <command.h>
 #include <image.h>
-#include <vxworks.h>
 #include <u-boot/zlib.h>
 #include <asm/byteorder.h>
 #include <libfdt.h>