I've done those conversions by hand before, just deleting irrelevant Google junk out of the KML file to import it to OsmAnd~ because I planned my route on the desktop Google Earth app (3D is cool) and exported it to KML. After some edits it usually will import to OsmAnd on the phone
If you ever need a 3D map on the phone, have a look at the OSM-based Magic Earth. You'll have to select a map style (in the General settings) with elevation, such as "Satellite 2 with Elevation and Streets".