games/openbve: the port had been updated (+)

- Update OpenBVE to version 1.8.1.0, which now supports routes from the
  legacy DOS simulator Mechanik, among other changes and bug fixes
- AssemblyInfo.sh (shell script) had been replaced with AssemblyInfo.tt
  written in C# which means gdate(1) is no longer used and we can drop
  the build-time dependency on the `sysutils/coreutils' port/package

Reported by:	portscout