Clean up high pT single muon line

The following discussion from !360 (merged) should be addressed:

• @gligorov started a discussion: (+7 comments)

  Very nice! Shouldn't this line be implemented without a GEC but with a different tuning of VeloUT and Forward tracking with tighter momentum search windows? I get that you're trying to do something simple here so if I didn't get the physics wrong feel free to resolve this to an issue.

To summarise, these are to be followed up:

• Remove GEC.
• Use tracking with modified thresholds.
• Tune cuts.
• Move the one_track_muon_highpt_line() to the main settings.py file once it is more mature.