Drop KNITRO@14 support

[odow]

Does anyone object? Now that we have the JLL stuff working, this would simplify a lot of things.

cc @amontoison?

[amontoison]

It is a good idea, I approve to drop support for KNITRO v14.x.

[odow]

We could, for example, fix #344 by doing #341.

This would also be a good excuse to make a breaking v1.0 release.

[amontoison]

Yes, you have my full support 👍
At the same time, we can clean up all checks on the KNITRO version number, such as:
https://github.com/jump-dev/KNITRO.jl/blob/master/ext/KNITROMathOptInterfaceExt.jl#L1652-L1654