[collectd/nginx] remove deprecated plugin

[atoulme]

Description:
Remove deprecated collectd/nginx plugin.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.01%. Comparing base (6e453cb) to head (e0102b0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7091      +/-   ##
==========================================
- Coverage   38.10%   38.01%   -0.10%     
==========================================
  Files         358      357       -1     
  Lines       25107    25099       -8     
==========================================
- Hits         9568     9542      -26     
- Misses      14746    14759      +13     
- Partials      793      798       +5     

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