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