Revert "Don't expose Go timers directly to lua"

This reverts commit 4ffc220.

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

internal/lua/lua.go

@@ -521,16 +521,21 @@ func importErrors() *lua.LTable {
 func importTime() *lua.LTable {
 	pkg := L.NewTable()
 
+	L.SetField(pkg, "After", luar.New(L, time.After))
 	L.SetField(pkg, "Sleep", luar.New(L, time.Sleep))
+	L.SetField(pkg, "Tick", luar.New(L, time.Tick))
 	L.SetField(pkg, "Since", luar.New(L, time.Since))
 	L.SetField(pkg, "FixedZone", luar.New(L, time.FixedZone))
 	L.SetField(pkg, "LoadLocation", luar.New(L, time.LoadLocation))
+	L.SetField(pkg, "NewTicker", luar.New(L, time.NewTicker))
 	L.SetField(pkg, "Date", luar.New(L, time.Date))
 	L.SetField(pkg, "Now", luar.New(L, time.Now))
 	L.SetField(pkg, "Parse", luar.New(L, time.Parse))
 	L.SetField(pkg, "ParseDuration", luar.New(L, time.ParseDuration))
 	L.SetField(pkg, "ParseInLocation", luar.New(L, time.ParseInLocation))
 	L.SetField(pkg, "Unix", luar.New(L, time.Unix))
+	L.SetField(pkg, "AfterFunc", luar.New(L, time.AfterFunc))
+	L.SetField(pkg, "NewTimer", luar.New(L, time.NewTimer))
 	L.SetField(pkg, "Nanosecond", luar.New(L, time.Nanosecond))
 	L.SetField(pkg, "Microsecond", luar.New(L, time.Microsecond))
 	L.SetField(pkg, "Millisecond", luar.New(L, time.Millisecond))