Remove MRB_METHOD_TABLE_INLINE.

`MRB_METHOD_TABLE_INLINE` was fragile. It requires `-falign-functions=n`.
On platform that uses higher bits of function pointers, you can use new
`MRB_METHOD_T_STRUCT` configuration macro.

include/mruby.h

@@ -188,7 +188,7 @@ struct mrb_context {
  */
 typedef mrb_value (*mrb_func_t)(struct mrb_state *mrb, mrb_value self);
 
-#ifdef MRB_METHOD_TABLE_INLINE
+#ifndef MRB_METHOD_T_STRUCT
 typedef uintptr_t mrb_method_t;
 #else
 typedef struct {