UPSTREAM: arm64: compat: Remove leftover variable declaration

(cherry picked from commit 82d24d114f249d919b918ff8eefde4117db8f088)

Commit a1d5eba ("arm64: big-endian: don't treat code as data when
copying sigret code") moved the 32-bit sigreturn trampoline code from
the aarch32_sigret_code array to kuser32.S. The commit removed the
array definition from signal32.c, but not its declaration in
signal32.h. Remove the leftover declaration.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Bug: 20045882
Bug: 63737556
Change-Id: Ic8a5f0e367f0ecd5c5ddd9e3885d0285f91cf89e

Author: kevin-brodsky-arm

arch/arm64/include/asm/signal32.h

@@ -22,8 +22,6 @@
 
 #define AARCH32_KERN_SIGRET_CODE_OFFSET	0x500
 
-extern const compat_ulong_t aarch32_sigret_code[6];
-
 int compat_setup_frame(int usig, struct ksignal *ksig, sigset_t *set,
 		       struct pt_regs *regs);
 int compat_setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,