Remove pump_loop_completed on reboot to make mmtune run sooner

[jaylagorio]

As noted in #630, I've never seen mmtune run sooner than on the fourth time through the loop after rebooting. Removing pump_loop_completed on reboot makes the loop run mmtune on the first loop, decreasing non-looping time from about 25 minutes after reboot to a little under 10 minutes.

[PieterGit]

@jaylagorio @scottleibrand : I see two other solutions that I think are cleaner than adding another crontab line.

1. rewrite pump_loop_completed to /tmp/pump_loop_completed. That way the cleaning isn't necessary because /tmp gets cleared by default on a reboot

2. rewrite the @reboot reset_spi_serial.py line to a single crontab line for all the pump init and mmtune, e.g.
   @reboot cd $directory ; openaps use pump init ; openaps use pump mmtune

I think I prefer option 2. I tried adding it to openaps once, but did not succeed yet.

[scottleibrand]

I like #1. One of you want to PR that?

[jaylagorio]

The search feature wasn't being my friend so the only place I found reference to that file was oref0-pump-loop.sh. If that's the only place it's used: #672