Don't expose Go timers directly to lua

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.

internal/lua/lua.go

@@ -523,21 +523,16 @@ 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))