powerpc: Remove -Wattribute-alias pragmas

With SYSCALL_DEFINEx() disabling -Wattribute-alias generically, there's
no need to duplicate that for PowerPC syscalls.

This reverts commit 4155203739 ("powerpc: fix build failure by
disabling attribute-alias warning in pci_32") and commit 2479bfc9bc
("powerpc: Fix build by disabling attribute-alias warning for
SYSCALL_DEFINEx").

Signed-off-by: Paul Burton <paul.burton@mips.com>
Acked-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/powerpc/kernel/signal_64.c

@@ -625,9 +625,6 @@ static long setup_trampoline(unsigned int syscall, unsigned int __user *tramp)
 /*
  * Handle {get,set,swap}_context operations
  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wpragmas"
-#pragma GCC diagnostic ignored "-Wattribute-alias"
 SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 		struct ucontext __user *, new_ctx, long, ctx_size)
 {
@@ -693,7 +690,6 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
 }
-#pragma GCC diagnostic pop
 
 
 /*