Theory covmat prescription still determined by length of theoryids

[RosalynLP]

I noticed that the theory covmat prescription in covs_pt_prescrip is determined still using the length of theoryids and whether or not "fivetheories" is set. Since the introduction of point_prescription to the runcard this seems like a non-ideal way to do things, especially since people will need to specify both

point_prescription: "5bar pt"
fivetheories: "bar"

to get it to work. A simple thing to do it move to pure reliance on point_prescription to tell the action what prescription to use, however this might deprecate some old runcards. I don't think this is so much of a problem as they weren't widely run by anyone other than me and @voisey, but it is something to be aware of.

If e.g. @voisey @Zaharid think it's OK I'd like to go ahead and update this.

[voisey]

Sorry for not replying to this until now, I somehow completely missed this. I would naively be in favour of removing fivetheories and making things reliant on point_prescription, which I agree would be a lot better. However, regarding how this would be with regards to backwards compatibility I would defer to @Zaharid

[scarlehoff]

This was (likely) fixed by #1524 or #1528