Remove useless migrator task generics

[jamesagnew]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@80139f4). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #1687   +/-   ##
========================================
  Coverage          ?   80.4%           
  Complexity        ?   13600           
========================================
  Files             ?     943           
  Lines             ?   51086           
  Branches          ?    8324           
========================================
  Hits              ?   41075           
  Misses            ?    6822           
  Partials          ?    3189

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