Strip unused variables on their way out

[AlecAivazis]

Fixes https://discord.com/channels/1024421016405016718/1268152875914104853

This PR fixes an issue when using the @parentID directive powered by a query variable. Before the variable would be sent along with the query (even tho it wasn't actually used). In some server runtimes, this causes an error.

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• [x] Update the first line to point to the ticket that this PR fixes
• [x] Add a message that clearly describes the fix
• [x] If applicable, add a test that would fail without this fix
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• [x] Includes a changeset if your fix affects the user with pnpm changeset

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🦋 Changeset detected

Latest commit: 34f24a5896761d0dc1ce29fd837f7db41c94e1f1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

| Name | Type | | ----------------------------------- | ----- | | houdini | Patch | | houdini-adapter-auto | Patch | | houdini-adapter-cloudflare | Patch | | houdini-adapter-node | Patch | | houdini-adapter-static | Patch | | houdini-react | Patch | | houdini-svelte | Patch | | houdini-plugin-svelte-global-stores | Patch | | create-houdini | Patch |

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