MODE-2303 Removed the "queryableBranches" feature of the Git Connector.

that was my first approach (i.e. deprecation) but custom component fields are always initialized via reflection direct field access. Meaning there is no way to print out a warning. This means that if we leave this in and ppl are actually using it, they'd expect the behavior.
On the other hand, failing with a meaningful exception is less misleading. 
It's worth mentioning that I doubt *anyone* is using this in 4.0, or we would've see this reported.