Fix dynamic knobs

[Hypnosphi]

Issue: #2661 accidentally broke "dynamic knobs" feature (storybook-eol/storybook-addon-knobs#59)

How to test

Open dynamic knobs story, select "no". Optionsl knob should disappear

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@da5fdef). Click here to learn what that means.
The diff coverage is 25%.

@@            Coverage Diff            @@
##             master    #3464   +/-   ##
=========================================
  Coverage          ?   37.23%           
=========================================
  Files             ?      464           
  Lines             ?    10289           
  Branches          ?      932           
=========================================
  Hits              ?     3831           
  Misses            ?     5909           
  Partials          ?      549

Impacted Files	Coverage Δ
addons/knobs/src/components/Panel.js	73.61% <25%> (ø)

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[shilman]

@Hypnosphi this PR doesn't seem to contain any changed files, but there are non-empty commits. Is this a github bug?

[Hypnosphi]

Looks like it's merged as a part of #3465
It would still make sense to cherry-pick d2a289e to release/3.4, will do that