Remove CNRN mechanism layout.

[1uc]

There's only one layout in CoreNEURON: SoA.

CI_BRANCHES:NMODL_BRANCH=1uc/remove-cnrn-mech-layout

[1uc]

Due to CI not refreshing, a second attempt at #2895.

[sonarcloud[bot]]

Quality Gate passed

Issues
104 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.7% Duplication on New Code

See analysis details on SonarCloud

[bbpbuildbot]

Logfiles from GitLab pipeline #217780 (:no_entry:) have been uploaded here!

Status and direct links:

• :white_check_mark: mac_m1_cmake_build: [cmake, ON, OFF, OFF, address]
• :no_entry: spack_setup
• :fast_forward: build:nmodl
• :fast_forward: build:neuron:nmodl:intel:legacy
• :fast_forward: build:neuron:nmodl:intel:shared
• :fast_forward: build:neuron:nmodl:nvhpc:acc:legacy
• :fast_forward: build:neuron:nmodl:nvhpc:acc:shared
• :fast_forward: build:neuron:nmodl:nvhpc:omp:legacy
• :fast_forward: build:neuron:nmodl:nvhpc:omp
• :fast_forward: test:neuron:nmodl:intel:legacy
• :fast_forward: test:neuron:nmodl:intel:shared
• :fast_forward: test:neuron:nmodl:nvhpc:acc:legacy
• :fast_forward: test:neuron:nmodl:nvhpc:acc:shared
• :fast_forward: test:neuron:nmodl:nvhpc:omp:legacy
• :fast_forward: test:neuron:nmodl:nvhpc:omp