fix: Makefile license header duplication

[ianlewis]

Description:

Removes duplicate license header in Makefile

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Add a note in the CHANGELOG.md if applicable.
• Sign the Google CLA.

[codecov]

Codecov Report

Merging #589 (e7a2058) into main (cc90c56) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #589   +/-   ##
=======================================
  Coverage   80.46%   80.46%           
=======================================
  Files          19       19           
  Lines        1121     1121           
  Branches       14       14           
=======================================
  Hits          902      902           
  Misses        157      157           
  Partials       62       62