* Revert "Don't expose Go timers directly to lua"
This reverts commit 4ffc2206ee.
Reason for revert: some plugins happen to use raw Go timers via
time.AfterFunc(), in an unsafe way (without synchronizing their
async code with micro). Let them keep doing that for now, in an
unsafe way but at least without immediate crashes.
Fixes#3209
* Add TODO about Go timers deprecation
Exposing locking primitives to lua plugins is tricky and may lead to
deadlocks. Instead, if possible, it's better to ensure all the needed
synchonization in micro itself, without leaving this burden to lua code.
Since we've added micro.After() timer API and removed exposing Go timers
directly to lua, now we (probably?) have no cases of lua code possibly
running asynchronously without micro controlling when it is running. So
now we can remove lua.Lock.
This means breaking compatibility, but, until recently lua.Lock wasn't
workable at all (see #2945), which suggests that it has never been
really used by anyone. So it should be safe to remove it.
Since we now expose our own micro.After() API which is more convenient
and safer to use than directly using Go timers, we can remove exposing
Go timers to lua directly.
