[ui] Remove json linting while editing variables

[philrenaud]

This removes the JSON Linting gutter highlight capabilities originally added in #13461

The main reason for this removal is the inclusion of a nested Underscore dependency: https://github.com/hashicorp/nomad/security/dependabot/110

However, our dependency (a grandparent of the insecure underscore version) has not been updated in quite some time and appears to be unmaintained.

As such, I've given consideration to whether this feature is worth forking, pinning, or abandoning. Per zaach/jsonlint#120 a change has been merged to master in jsonlint, but no release on npm has been made. As such, I've opted to remove the feature for the same reasons other projects have done so: it doesn't give enough benefit to warrant hanging on to an un-updated dependency for marginal utility.

[tgross]

LGTM! (once tests are green) This was a nice to have but if someone is really having trouble with it, the form-editor interface is still there instead of the JSON mode. And it's all ultimately validated server side.

[philrenaud]

LGTM! (once tests are green) This was a nice to have but if someone is really having trouble with it, the form-editor interface is still there instead of the JSON mode. And it's all ultimately validated server side.

Even better, it'll still run a JSON.parse() on user input on keypress, so the user will still get output like this before ever hitting the server:

(It just won't be the pretty code-mirror-gutter style lint errors that showed exact position, etc.)

[github-actions]

Ember Test Audit comparison

	main	2f19e0e	change
passes	1550	1550	0
failures	0	0	0
flaky	0	0	0
duration	10m 47s 484ms	10m 51s 067ms	+03s 583ms

[github-actions]

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