Remove custom singleton mutex name option

[shreyamalviya]

What does this PR do?

#1537

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?

Testing Checklist

• Added relevant unit tests?
• Have you successfully tested your changes locally? Elaborate:

  Tested by {Running the Monkey locally with relevant config/running Island/...}

• If applicable, add screenshots or log transcripts of the feature working

Explain Changes

Are the commit messages enough? If not, elaborate.

[codecov]

Codecov Report

Merging #1589 (f90434d) into develop (6f4c671) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #1589      +/-   ##
===========================================
- Coverage    44.76%   44.75%   -0.01%     
===========================================
  Files          474      474              
  Lines        13856    13855       -1     
===========================================
- Hits          6202     6201       -1     
  Misses        7654     7654              

Impacted Files	Coverage Δ
monkey/infection_monkey/config.py	61.71% <ø> (-0.30%)	⬇️
monkey/infection_monkey/system_singleton.py	0.00% <0.00%> (ø)
...onkey_island/cc/services/config_schema/internal.py	100.00% <ø> (ø)

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