fix: removes rr7 warn on dev.ts

[andguy95]

WHY are these changes introduced?

The React Router v7 version check was generating inaccurate warnings during shopify hydrogen dev because it was not correctly checking what was actually resolved in node_modules. This caused confusion for developers who had valid React Router installations but were still seeing version mismatch warnings.

WHAT is this pull request doing?

Removes the React Router v7 version compatibility check from the Hydrogen dev command:

• Deletes packages/cli/src/lib/react-router-version-check.ts — the utility that compared RR7 package versions against an expected 7.12.0 baseline
• Removes the checkReactRouterVersions() call from packages/cli/src/commands/hydrogen/dev.ts

HOW to test your changes?

1. Run shopify hydrogen dev in the templates/skeleton folder
2. You should no longer see the error

Note** this will require you to test this hydrogen-cli change with the Shopify CLI local override workaround

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[shopify]

Oxygen deployed a preview of your an-removes-rr7-warn branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 24, 202611:53 PM

Learn more about Hydrogen's GitHub integration.

[fredericoo]

nittiest of nits: this will be read by people after the change has been made

write it in the past form when possible: "Removes" → "Removed", or even "No longer warn about react router versions when starting the dev server"

[fredericoo]

just a nit on the changesets but it’s great!