feat(checks): deprecate aria-busy check (#4356)

axe-core's only usage of the `aria-busy` check was just removed in
#4347, so this check is no longer required.

See #4340

Author: dbjorge

lib/checks/aria/aria-busy.json

@@ -1,6 +1,7 @@
 {
   "id": "aria-busy",
   "evaluate": "aria-busy-evaluate",
+  "deprecated": true,
   "metadata": {
     "impact": "serious",
     "messages": {