Truncated routes cause unhandled exceptions

[FelixDuxNATS]

This was observed on the develop branch running with --simtype machcoll.

I generated sector and scenario files using the latest aviary develop branch (using the example commands in the README.md). In the scenario, aviary correctly truncates the routes to remove fixes that have already been passed (based on the start location), but the consequence is that the routes in the scenario no longer exactly match the sequences of fixes in the predefined routes in the sector file. This causes an unhandled exception at line 197 of bluebird/sim_proxy/proxy_aircraft_controls.py. The two routes in the scenario visit the following sequences of fixes:

• GATES, ABYSS, HAUNT, LIMBO – which is route BLASPHEMER minus the first fix (SIN)
• HAUNT, ABYSS, GATES, SIN – which is route PURGATORY minus the first fix (LIMBO)