UPSTREAM: arm64: compat: Remove leftover variable declaration

(cherry picked from commit 82d24d114f249d919b918ff8eefde4117db8f088)

Commit a1d5ebaf8ccd ("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
Signed-off-by: Mister Oyster <oysterized@gmail.com>