Use default low_threshold and high_threshold

[maurolepore]

While thresholds remain unparametrized (#23) it's safest to use the defaults.

Currently the workflows profile_sector*.Rmd use the wrong *threshold, and it also makes this package harder to maintain -- because when the default *threshold change upstream (e.g. in tiltIndicator) we need to remember to update the values used in each workflow. It's best to remove the *threshold and let each profile*() use the defaults.

Here's the biggest problem, compare:

Good: Helpfile

Bad: Workflow