arm64: Remove orphaned __addr_ok() definition

Since commit 12a0ef7b ("arm64: use generic strnlen_user and
strncpy_from_user functions"), the definition of __addr_ok() has been
languishing unused; eradicate the sucker.

CC: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/uaccess.h

@@ -80,19 +80,6 @@ static inline void set_fs(mm_segment_t fs)
 
 #define segment_eq(a, b)	((a) == (b))
 
-/*
- * Return 1 if addr < current->addr_limit, 0 otherwise.
- */
-#define __addr_ok(addr)							\
-({									\
-	unsigned long flag;						\
-	asm("cmp %1, %0; cset %0, lo"					\
-		: "=&r" (flag)						\
-		: "r" (addr), "0" (current_thread_info()->addr_limit)	\
-		: "cc");						\
-	flag;								\
-})
-
 /*
  * Test whether a block of memory is a valid user space address.
  * Returns 1 if the range is valid, 0 otherwise.