move/cleanup exporter examples

[brettmc]

• moving exporter examples up one directory, where I think they are more obvious to find
• remove some old and broken grpc examples
• remove unused interface

[codecov]

Codecov Report

Merging #886 (b7a6f17) into main (587bc5a) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #886   +/-   ##
=========================================
  Coverage     81.56%   81.56%           
  Complexity     2008     2008           
=========================================
  Files           264      264           
  Lines          5219     5219           
=========================================
  Hits           4257     4257           
  Misses          962      962           

Flag	Coverage Δ
7.4	81.05% <ø> (ø)
8.0	81.55% <ø> (ø)
8.1	81.69% <ø> (ø)

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[pdelewski]

Seems that features is a container for examples that do not belongs to any other category