arm64: extable: remove unused ex_handler_t definition

The ex_handler_t type was introduced in commit d6e2cc56 ("arm64:
extable: add `type` and `data` fields"), but has never been used, and
is unnecessary. Remove it.
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20211119124608.3f03380b@xhackerSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/extable.c

@@ -10,9 +10,6 @@
 #include <asm/asm-extable.h>
 #include <asm/ptrace.h>
 
-typedef bool (*ex_handler_t)(const struct exception_table_entry *,
-			     struct pt_regs *);
-
 static inline unsigned long
 get_ex_fixup(const struct exception_table_entry *ex)
 {