drop dependencies for retired / deprecated packages

[achubaty]

• s-u/fastshp hasn't seen updates in a very long time and no longer compiles for modern R versions;
• SDMTools is orphaned and archived on CRAN (as a stopgap, use https://github.com/achubaty/SDMTools);
• use qs2 instead of qs (transition from qs to qs2 #131);
• rgdal, rgeos, and maptools have been retired (update geospatial packages #132);