remove all Threads.threadid()

[MarcMush]

fix #338

threadid() was only used in tests, to make sure that all threads are being used when testing

is there really a need to test how the threading is done?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.77%. Comparing base (807496a) to head (74e4e23).
Report is 22 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   93.48%   96.77%   +3.29%     
==========================================
  Files           1        1              
  Lines         399      559     +160     
==========================================
+ Hits          373      541     +168     
+ Misses         26       18       -8     

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