Remove nested fields in remove_fields plugin

[goshansmails]

Fixes #651

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.61702% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.28%. Comparing base (67ecc39) to head (e760e7c). Report is 21 commits behind head on master.

:exclamation: Current head e760e7c differs from pull request most recent head 234f8d3

Please upload reports for the commit 234f8d3 to get more accurate results.

Files	Patch %	Lines
plugin/action/remove_fields/remove_fields.go	93.61%	2 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #652      +/-   ##
==========================================
+ Coverage   70.83%   71.28%   +0.44%     
==========================================
  Files         124      131       +7     
  Lines       12572    13088     +516     
==========================================
+ Hits         8906     9330     +424     
- Misses       3150     3226      +76     
- Partials      516      532      +16     

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