tools: Improve speed of tools/changelogger-release.sh

[anomiex]

Proposed changes:

The script has gotten a bit slow, since it was running check-intra-monorepo-deps.sh individually for each project to pass either -u or -U depending on whether the project was included in the release or not.

We can speed it up by running check-intra-monorepo-deps.sh -U just once, and then looking at the git diff to see whether any changelog entries seem to be needed.

Also, we can then drop the PACKAGE_VERSIONS_CACHE thing from check-intra-monorepo-deps.sh that was done in a prior speedup attempt.

And finally, skip trying to handle the "monorepo" pseudo-package, it won't work and prevents releases of projects depended on by the monorepo root.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Try it out. I did so myself to create Release various packages that haven't been released in a while #39145, FWIW.

[github-actions]

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