Deprecate and remove ErrorFlyout from Gestalt

[pfarejowicz]

Now that we have a release that allows clients to create an ErrorFlyout-like component via the Flyout props, we can fully deprecate and remove the ErrorFlyout component in the next release. This change removes all references to that component and removes it from the export.

Snapshots did not change which is a good sign that nothing visually changes in the UI with this switch 👍

[christianvuerings]

Deploy preview for gestalt ready!

Built with commit 559d882

https://deploy-preview-251--gestalt.netlify.com

[codecov-io]

Codecov Report

Merging #251 into master will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #251      +/-   ##
==========================================
- Coverage   70.73%   70.55%   -0.18%     
==========================================
  Files          46       45       -1     
  Lines         820      815       -5     
  Branches      189      188       -1     
==========================================
- Hits          580      575       -5     
  Misses        169      169              
  Partials       71       71

Impacted Files	Coverage Δ
packages/gestalt/src/TextField/TextField.js	42.1% <ø> (ø)	⬆️
packages/gestalt/src/TextArea/TextArea.js	35% <ø> (ø)	⬆️

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[ghost]

Filename	Size Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip
gestalt.js	🔻 0.1%	🔻 0.1%	268.36 KB	268.08 KB	59.54 KB	59.46 KB
gestalt.es.js	🔻 0.1%	🔻 0.1%	265.73 KB	265.44 KB	59.18 KB	59.1 KB

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