DelegatingMarker.remove should call map.onRemove *before* real.remove

=> DelegatingGoogleMap.onRemove(DelegatingMarker marker) calls
createdMarkers.remove(marker.getReal().getMarker()), but getMarker()
always returns null at this point if the marker is removed before
calling onRemove, since LazyMarker#remove nulls it.
Merge remote-tracking branch 'yochiro/fix'