Remove references to self._container from within onAdd()

As described in our internal ticket RIMS-550, this removes references to `self._container` from within onAdd() since `self._container` is not defined the first time `onAdd` is executed. All other changes that we have made in our local usage of `L.Control.Locate.js` have been included.

Also as mentioned in our in-house ticket, if this is actually a bad thing and will not be used as such on our server, no need to accept this. I just wanted to make sure our repo of monkeypatched code was up to date with our actual usage.