Drop "Install latest yarn version" step on CI

[Hypnosphi]

It's now part of official node docker image

[codecov]

Codecov Report

Merging #1910 into release/3.3 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           release/3.3    #1910   +/-   ##
============================================
  Coverage        22.24%   22.24%           
============================================
  Files              325      325           
  Lines             6519     6519           
  Branches           830      816   -14     
============================================
  Hits              1450     1450           
- Misses            4454     4464   +10     
+ Partials           615      605   -10

Impacted Files	Coverage Δ
app/react/src/server/config/babel.js	0% <0%> (-100%)	⬇️
...tories_panel/stories_tree/tree_decorators_utils.js	45.23% <0%> (ø)	⬆️
app/react/src/client/preview/error_display.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/components/menu_item.js	19.14% <0%> (ø)	⬆️
addons/knobs/src/components/PropField.js	10.86% <0%> (ø)	⬆️
addons/info/src/components/types/PrettyPropType.js	10.2% <0%> (ø)	⬆️
addons/info/src/components/types/PropertyLabel.js	21.05% <0%> (ø)	⬆️
...react-native/src/manager/components/PreviewHelp.js	0% <0%> (ø)	⬆️
addons/info/src/components/types/Enum.js	0% <0%> (ø)	⬆️
addons/info/src/components/Node.js	39.7% <0%> (ø)	⬆️
... and 25 more

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[ndelangen]

Perfect!