Remove unused fakeMessage helper methods

[stewartboyd119]

1. Remove unused fakeMessage helper methods (leave and deprecate the popular zillow one)1
2. Remove unused benchmark
3. Remove zgkafka specific headers (rely on composition root for enterprise specific headers)

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 89.39394% with 7 lines in your changes missing coverage. Please review.

Project coverage is 93.19%. Comparing base (7935b74) to head (e3ced13).

Files	Patch %	Lines
testhelper.go	88.09%	3 Missing and 2 partials ⚠️
message.go	91.30%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
- Coverage   93.78%   93.19%   -0.60%     
==========================================
  Files          17       17              
  Lines        1288     1278      -10     
==========================================
- Hits         1208     1191      -17     
- Misses         52       56       +4     
- Partials       28       31       +3     

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