Prune non-go files from vendoring

[mboersma]

What this PR does / why we need it:

Removes 218 unnecessary files from the vendor/ directory. See also Azure/aks-engine#43.

See https://github.com/golang/dep/blob/master/docs/Gopkg.toml.md#prune for information about pruning vendored files with dep.

Special notes for your reviewer:

If applicable:

• [ ] documentation
• [ ] unit tests
• [ ] tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

Prune non-go files from vendoring

[tariq1890]

/lgtm

[codecov[bot]]

Codecov Report

Merging #4320 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4320   +/-   ##
=======================================
  Coverage   55.45%   55.45%           
=======================================
  Files         109      109           
  Lines       16053    16053           
=======================================
  Hits         8902     8902           
  Misses       6368     6368           
  Partials      783      783

[codecov[bot]]

Codecov Report

Merging #4320 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4320   +/-   ##
=======================================
  Coverage   55.45%   55.45%           
=======================================
  Files         109      109           
  Lines       16053    16053           
=======================================
  Hits         8902     8902           
  Misses       6368     6368           
  Partials      783      783