Remove build parameter 'useTransfersTxt'

[leonardehrenfried]

Summary

As discussed in the dev meeting today we decided the parameter useTransfersTxt. Reasons for removal are the following:

• the name is wrong: it doesn't enable or disable the transfers.txt but the calculation of the OSM transfers
• none of us found a use case were turning off the OSM transfers was a good idea

Instead we want to implement a fallback logic like this:

• if we have a transfer in transfers.txt use that
• if not then use pathways.txt
• if not then use OSM based transfers

This will happen in a separate PR.

Issue

n/a

Unit tests

n/a

Code style

Yes.

Documentation

Documentation removed.