Removing phone param

What does this MR do and why?

We're not passing the phone param in the in-instance self-managed trial form anymore, so this removes the param.

References

• https://gitlab.com/groups/gitlab-org/-/work_items/20281

Screenshots or screen recordings

Before	After

How to set up and validate locally

You can find the form using these steps:

1. Restart GDK in self managed
   1. export GITLAB_SIMULATE_SAAS=0
2. Enable the Feature flag
   1. Go to http://127.0.0.1:3000/rails/features/
   2. Search and enable automatic_self_managed_trial_activation
3. Log in as administrator
4. Go to: http://127.0.0.1:3000/admin/subscription
   1. Click "Start Free Trial"
   2. You will be redirected to http://127.0.0.1:3000/-/trials/new and you see the above (screenshot) form

MR acceptance checklist

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