ARC: Delete stale barrier.h

Commit 93ea02bb84 ("arch: Clean up asm/barrier.h implementations")
wired generic barrier.h for ARC, but failed to delete the existing file.

In 3.15, due to rcupdate.h updates, this causes a build breakage on ARC:

      CC      arch/arc/kernel/asm-offsets.s
    In file included from include/linux/sched.h:45:0,
                     from arch/arc/kernel/asm-offsets.c:9:
    include/linux/rculist.h: In function __list_add_rcu:
    include/linux/rculist.h:54:2: error: implicit declaration of function smp_store_release [-Werror=implicit-function-declaration]
      rcu_assign_pointer(list_next_rcu(prev), new);
      ^

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arc/include/asm/barrier.h

@@ -1,37 +0,0 @@
-/*
- * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-
-#ifndef __ASM_BARRIER_H
-#define __ASM_BARRIER_H
-
-#ifndef __ASSEMBLY__
-
-/* TODO-vineetg: Need to see what this does, don't we need sync anywhere */
-#define mb() __asm__ __volatile__ ("" : : : "memory")
-#define rmb() mb()
-#define wmb() mb()
-#define set_mb(var, value)  do { var = value; mb(); } while (0)
-#define set_wmb(var, value) do { var = value; wmb(); } while (0)
-#define read_barrier_depends()  mb()
-
-/* TODO-vineetg verify the correctness of macros here */
-#ifdef CONFIG_SMP
-#define smp_mb()        mb()
-#define smp_rmb()       rmb()
-#define smp_wmb()       wmb()
-#else
-#define smp_mb()        barrier()
-#define smp_rmb()       barrier()
-#define smp_wmb()       barrier()
-#endif
-
-#define smp_read_barrier_depends()      do { } while (0)
-
-#endif
-
-#endif