Remove not used file about Pypy

[RubenRubens]

Is registering.txt relevant today? Back in the day it was valuable to Dave Cowden. Maybe we should just remove it.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@a71a93e). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #733   +/-   ##
=========================================
  Coverage          ?   94.56%           
=========================================
  Files             ?       32           
  Lines             ?     7218           
  Branches          ?      786           
=========================================
  Hits              ?     6826           
  Misses            ?      257           
  Partials          ?      135           

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[jmwright]

Thanks again @RubenRubens