ISISDATA area contains outdated monthly CTX calibration files

**Description**
After syncing the Isisdata area using downloadIsisData, I see a folder called `ctxFlatFiles` inside `mro/calibration`. As I'm the author of these files, I know that they are outdated. The new calibration is established in the file `ctxFlat_0003.cub` and supersedes the monthly calibration files. The folder `ctxFlatFiles` should be deleted from the Isis data area. It is not harmful, but confusing.

**Possible Solution**
Delete folder `ctxFlatFiles`from `$ISISDATA/mro/calibration`

**Additional context**
See Issue #5279