remove unused functions

[valentinsulzer]

Description

Remove some functions that aren't used anywhere

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Base: 99.66% // Head: 99.66% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (ab9aec4) compared to base (c89445e).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2384      +/-   ##
===========================================
- Coverage    99.66%   99.66%   -0.01%     
===========================================
  Files          269      269              
  Lines        20206    20173      -33     
===========================================
- Hits         20139    20106      -33     
  Misses          67       67              

Impacted Files	Coverage Δ
pybamm/discretisations/discretisation.py	99.80% <ø> (-0.01%)	⬇️
pybamm/models/base_model.py	98.52% <ø> (-0.03%)	⬇️
pybamm/util.py	100.00% <ø> (ø)

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[brosaplanella]

Looks good, thanks!