Merge pull request #2994 from RosettaCommons/vmullig/correct_flag_error
Promoting warning about -correct flag to an actual error.
Users have been using the `-correct` flag with `ref2015` without realizing that this results in invalid behaviour. The warning message is easily missed. This promotes it to an error, so that they can't use it accidentally.
A small handful of score12-era integration tests were also still using the `-correct` flag despite having been updated to use `ref2015`. These now correctly do _not_ use `-correct`. This will result in some integration test changes.