Remove GossipMessage protobuf

[Stefan-Ethernal]

Description

Removes GossipMessage protocol buffer as it is not used and TransportMessage is used instead.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (feature/v3-parity@e993b3b). Click here to learn what that means.
The diff coverage is n/a.

@@                 Coverage Diff                  @@
##             feature/v3-parity    #1057   +/-   ##
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  Coverage                     ?   54.93%           
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  Files                        ?      169           
  Lines                        ?    22768           
  Branches                     ?        0           
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  Hits                         ?    12507           
  Misses                       ?     9269           
  Partials                     ?      992           

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