Navit: change repo to github; build R6255

The Navit development has recently moved from the sourceforge to github, hereby we reflect that change and pick up a fresh version.

Also disable old svn based versions build. Navit builds fetch version code from the version control system. So older versions require the code to be fetched with svn.

The build with fdroidserver succeeds: https://ci.gitlab.com/projects/6741/builds/234741