Revert "Hexagon: fix signal.c compile error"

This reverts commit f3f601c1.

UAPI headers cannot use "uapi/" in their paths by design -- when they're
installed, they do not have the uapi/ prefix.  Otherwise doing so breaks
userland badly.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Richard Kuo <rkuo@codeaurora.org>

arch/hexagon/include/uapi/asm/signal.h

@@ -19,8 +19,6 @@
 #ifndef _ASM_SIGNAL_H
 #define _ASM_SIGNAL_H
 
-#include <uapi/asm/registers.h>
-
 extern unsigned long __rt_sigtramp_template[2];
 
 void do_signal(struct pt_regs *regs);