Agent: Remove caching from get_agent_id()

[cakekoa]

What does this PR do?

Fixes #3119.

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?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Do all unit tests pass?
• Do all end-to-end tests pass?
• Any other testing performed?

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

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

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (eb3abd8) 72.33% compared to head (a1bfc9c) 72.32%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3162      +/-   ##
===========================================
- Coverage    72.33%   72.32%   -0.01%     
===========================================
  Files          462      462              
  Lines        13203    13200       -3     
===========================================
- Hits          9550     9547       -3     
  Misses        3653     3653              

see 1 file with indirect coverage changes

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