vendor: rename leftover vendor/ directory

[ahmetb]

Forgot to clean this up while resolving merge conflicts.

/kind cleanup
/assign @corneliusweig

[corneliusweig]

/lgtm
/approve

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[codecov-io]

Codecov Report

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The diff coverage is n/a.

@@           Coverage Diff            @@
##             master    #241   +/-   ##
========================================
  Coverage          ?   53.6%           
========================================
  Files             ?      16           
  Lines             ?     735           
  Branches          ?       0           
========================================
  Hits              ?     394           
  Misses            ?     289           
  Partials          ?      52

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