Remove stop controller endpoint

[aledbf]

What this PR does / why we need it:

Removes the /stop endpoint. This is something introduced in the first versions of the controller.
Related to #4052

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@1bd3fd2). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #4100   +/-   ##
=========================================
  Coverage          ?   57.75%           
=========================================
  Files             ?       87           
  Lines             ?     6488           
  Branches          ?        0           
=========================================
  Hits              ?     3747           
  Misses            ?     2311           
  Partials          ?      430

Impacted Files	Coverage Δ
cmd/nginx/main.go	6.71% <ø> (ø)

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[ElvinEfendi]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, ElvinEfendi

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