Remove nocmodl from nrnivmodl-cmake?

[D-McDougall]

Follow up to PR #3468

Overview of the change

Currently, nrnivmodl-cmake supports both nocmodl and NMODL.
It sure would be convenient to remove nocmodl from nrnivmodl-cmake

Pros:

• Fewer features makes it faster to develop.
• We don't spent time developing for nocmodl, which will be removed eventually.

Cons:

• I don't think anyone had big plans for using nrnivmodl-cmake with nocmodl?
• For testing, it might be nice to have two implementations of nrnivmodl, but then again that means twice as much code to test...

[nrnhines]

Maybe not related but it seems strange that nrnivmodl-all-cmake is also installed. I don't know what it is for although I see it called from several scripts.

[D-McDougall]

The program "nrnivmodl-all-cmake" builds both neuron and coreNeuron,
Whereas "nrnivmodl-cmake" only builds for neuron.

Both of these files are generated from "nrn/bin/nrnivmodl-cmake.in"

The only difference between these files is a single command line flag for cmake: -DNRNIVMODL_CORENEURON