spTransform only has character method

needs a revisit (and rewording the message)

```R
 p1
CRS arguments:
 +proj=laea +lat_0=56 +lon_0=-2.6 +x_0=0 +y_0=0 +datum=WGS84 +units=km
+no_defs 
> spTransform(walrus818, p1)
Error: trip doesn't use sp/rgdal spTransform now
 (warning in case you should do your own reprojection with sf or whatever)
> spTransform(walrus818, p1@projargs)


```