Update extensions.json

[tfroment]

cancel deprecation of CSS Peek extension:
EclipseFdn/open-vsx.org#3540

• I have read the note above about PRs contributing or fixing extensions
• I have tried reaching out to the extension maintainers about publishing this extension to Open VSX (if not, please create an issue in the extension's repo using this template).
• This extension has an OSI-approved OSS license (we don't accept proprietary extensions in this repository)

Description

This PR introduces X change for Y reason.

[tfroment]

@amvanbaren can you approve?

[filiptronicek]

Hey @tfroment 👋, and thanks for the contribution. It looks like this has been a mistake on my part where I accidentally marked the extension as deprecated last October. I'm not really sure how it came to be, possibly because of confusion with another extension (possibly the deprecated martinkchang.vscode-marko-peek), but this looks like an easy enough fix to go with, so let's ship it.

I will take the liberty to remove the line out of the file entirely, since we don't really use false with anything else in the file and omitting it should be enough.

Also, nice to meet you! Hope we can find some time to chat in the near future