Self Check Using Checker Warning

[noschiff]

I don't think it's a great idea to bind the presence of a checker warning to a requirement being a self check. I think there are times where we might want to add a warning without giving the freedom of a self check. For example, in #687, I added the two options for the Experimental Physics Lab requirement. The alternate option requires that "the experiments in PHYS 4400 do not overlap with those…" and I think that this could be better served by a warning. Would removing the connection between a warning and being a self check cause any problems?

I came across this while investigating #672 …