Remove colon variants on error messages

[JsonFreeman]

There are a number of error messages that have two almost identical variants. One with a colon at the end, and one with a period. The idea is that the error should end in a colon if has an elaboration, and a period if not. This is not giving us enough benefit to justify the existence of these variants. So we should remove the colon variants.

[DanielRosenwasser]

Duplicate of #107, but this just shows how annoying it is.