Possible bugs: Unused Variables

Discovered via GDPR Audit

https://github.com/Automattic/jetpack/blob/e26217c3de9a5f444627ccb3b89886e0ef1c5da1/modules/contact-form/admin.php#L555

`$grunion_form`

https://github.com/Automattic/jetpack/blob/e26217c3de9a5f444627ccb3b89886e0ef1c5da1/modules/contact-form/admin.php#L592-L593

`$to` and `$subject`

https://github.com/Automattic/jetpack/blob/04fbdf4430dce0c6c41ad390b6fbaaf3b3911ba8/modules/contact-form/grunion-contact-form.php#L1909

`$comment_author_url_label`

https://github.com/Automattic/jetpack/blob/04fbdf4430dce0c6c41ad390b6fbaaf3b3911ba8/modules/contact-form/grunion-contact-form.php#L1915

`$comment_content_label`

https://github.com/Automattic/jetpack/blob/04fbdf4430dce0c6c41ad390b6fbaaf3b3911ba8/modules/contact-form/grunion-contact-form.php#L2457

I believe this was supposed to be `$this->error = `

Inspect the cited assignments in modules/contact-form/admin.php and modules/contact-form/grunion-contact-form.php, then search for uses of each listed variable. Confirm which variables are genuinely unused and whether the line near grunion-contact-form.php:2457 should assign to $this->error; done means correcting or removing only the confirmed issues without changing contact-form behavior.

Written by the indexing model from the issue text.