Simplify computation of neuronhome paths

[alkino]

Needed for #2848 and still nice to have

[azure-pipelines]

✔️ 85f602d -> Azure artifacts URL

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.20%. Comparing base (4a1e15a) to head (1082c4b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2874   +/-   ##
=======================================
  Coverage   67.20%   67.20%           
=======================================
  Files         563      563           
  Lines      104247   104253    +6     
=======================================
+ Hits        70058    70065    +7     
+ Misses      34189    34188    -1     

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[sonarcloud]

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[azure-pipelines]

✔️ 1082c4b -> Azure artifacts URL

[bbpbuildbot]

Logfiles from GitLab pipeline #210253 (:white_check_mark:) have been uploaded here!

Status and direct links:

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

[JCGoran]

Other than the minor comments, LGTM.