treesitter: use internal "decorations" buffer

src/nvim/globals.h

@@ -127,10 +127,6 @@ typedef off_t off_T;
 EXTERN int mod_mask INIT(= 0x0);                /* current key modifiers */
 
 
-// TODO(bfredl): for the final interface this should find a more suitable
-// location.
-EXTERN sattr_T *lua_attr_buf INIT(= NULL);
-EXTERN size_t lua_attr_bufsize INIT(= 0);
 EXTERN bool lua_attr_active INIT(= false);
 
 /*