chore(pluginutils): remove unused peer dependency

[remcohaszing]

Rollup Plugin Name: @rollup/pluginutils

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

refs mdx-js/mdx#2671

Description

@rollup/pluginutils declares a peer dependency on rollup. However, it doesn’t actually use this dependency anywhere.

[shellscape]

@CharlieHelps please do a thorough review of this PR to determine if it's ready to merge. Look at the diff, reviews, comments, and referenced issues/docs/links to build a complete understanding. Then respond with a comment that includes a list of MUST fix items that must be fixed before the the PR is merged, and a list of IMPROVEMENTS that shouldn't block the merge but may be quick improvements or things that could be addressed in a follow up PR. The MUST fix items should explain exactly what's wrong and what needs to change to resolve the problem. Both should be numbered lists and the IMPROVEMENTS list should continue counting up from the MUST list. It's OK if there are no IMPROVEMENTS or MUST fix items, you can just omit the lists.

[charliecreates]

I did a full review of the diff, existing PR comments/reviews, and the referenced issue (mdx-js/mdx#2671).

MUST fix

1. Workflow gates are unresolved (action_required) on the current head commit.
   The PR is currently blocked, and required workflows have not actually executed for the head SHA because runs are waiting for approval/re-run. This means merge-readiness checks are not complete.
   What needs to change: A maintainer needs to approve/re-run the workflows for this fork PR, and all required checks must pass on the current head SHA before merge.

2. The PR title does not match this repo’s enforced title format.
   The current title (Remove unused peer dependency from pluginutils) does not match the regex enforced by the Pull Request Title Format workflow.
   What needs to change: Rename the PR title to match the configured pattern (for example: chore(pluginutils): remove unused rollup peer dependency) and re-run checks.

[shellscape]

@remcohaszing thanks for the PR. while it might be attractive to use the pluginutils package outside of rollup, the peerDep here matches dep enforcement with other plugins/packages in the repo, and enforces a contract. We're going to decline this PR for the moment.