gtfs2pt.py: retire code path for alternative mapperlib?

[namdre]

the fcd-process-chain that can be used as mapperlib has not been in use for several reasons

• it is proprietary and thus not as easy to use
• it's tailored to mapping somewhat dense fcd-data instead of very spare gtfs-station data
• it does not profit from the many speed-ups and routingType-guidance extensions supported by sumolib.route.mapTrace

retiring this code path could greatly simplify gtfs2pt (i.e. no more writing of intermediate fcd files) and potentially speed up procession due to eliminated xml writing and parsing.

@behrisch discuss!

[behrisch]

I agree. Probably no one uses the external lib anymore since the trace mapper got that fast.