kprobes/x86: Remove stale ARCH_SUPPORTS_KPROBES_ON_FTRACE define

Commit e7dbfe3 ("kprobes/x86: Move ftrace-based kprobe code
into kprobes-ftrace.c") switched from using
ARCH_SUPPORTS_KPROBES_ON_FTRACE to CONFIG_KPROBES_ON_FTRACE but
missed removing the define.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: masami.hiramatsu.pt@hitachi.com
Cc: ananth@in.ibm.com
Cc: a.p.zijlstra@chello.nl
Cc: fweisbec@gmail.com
Cc: rostedt@goodmis.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/kprobes.h

@@ -27,7 +27,6 @@
 #include <asm/insn.h>
 
 #define  __ARCH_WANT_KPROBES_INSN_SLOT
-#define  ARCH_SUPPORTS_KPROBES_ON_FTRACE
 
 struct pt_regs;
 struct kprobe;