[chore] Remove abandoned test certificates

[dmitryax]

Tests using them were removed https://github.com/open-telemetry/opentelemetry-collector/pull/11611/files#diff-f0afaeb39ee2513003060e3955fb8707fc18d974c11cd7641739690e211dd71d

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.54%. Comparing base (9dd4a5a) to head (b0b481c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12397   +/-   ##
=======================================
  Coverage   91.54%   91.54%           
=======================================
  Files         467      467           
  Lines       25618    25618           
=======================================
  Hits        23451    23451           
  Misses       1768     1768           
  Partials      399      399           

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