[test] Update Gromacs reference value

[victorusu]

Additionally, I have removed the obsolete Monch tests.

[teojgo]

Remove the super().__init__() from the base class.

[codecov-io]

Codecov Report

Merging #950 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #950      +/-   ##
==========================================
- Coverage   91.64%   91.64%   -0.01%     
==========================================
  Files          79       79              
  Lines       10482    10492      +10     
==========================================
+ Hits         9606     9615       +9     
- Misses        876      877       +1

Impacted Files	Coverage Δ
reframe/core/pipeline.py	93.77% <0%> (-0.14%)	⬇️
reframe/frontend/cli.py	80.32% <0%> (+0.06%)	⬆️
reframe/core/runtime.py	88.35% <0%> (+0.24%)	⬆️

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[vkarak]

Remove the super().__init__() from the base class.

@victorusu If you do that, make sure to decorate your test with @required_version(...), because this is quite recent change.

[vkarak]

lgtm