xtensa: remove xtensa asm unused header

1. this header is no use for asm

2. if use xclib, this header include xclib stdbool, and expand to typedef

Signed-off-by: honglin leng <[email protected]>

Author: lenghonglin

arch/xtensa/core/xtensa-asm2-util.S

@@ -5,7 +5,6 @@
  */
 #include <xtensa-asm2-s.h>
 #include <offsets.h>
-#include <zephyr/toolchain.h>
 #include <zsr.h>
 
 /*