chore: delete Node 8 presubmit tests

[fhinkel]

No description provided.

[codecov]

Codecov Report

Merging #1053 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1053   +/-   ##
=======================================
  Coverage   95.11%   95.11%           
=======================================
  Files          24       24           
  Lines       10767    10767           
  Branches      494      513   +19     
=======================================
  Hits        10241    10241           
  Misses        523      523           
  Partials        3        3           

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