Unsettled function bug in hook function

[rhansen]

See ether/etherpad#4880

cc @meaz

[JohnMcLear]

This warning no longer fires: commit 5a62f5a removed the cb parameter from aceEditEvent, so the hook's arity is now 2 and Etherpad's framework stops checking for the unsettled-function condition (see hooks.ts L142 — the warning only triggers for hook_fn.length >= 3). Closing as already fixed.