Remove A/B test code from Cody signup flow

[iskyOS]

Context
In this prior request, we added a new signup flow for Cody as an A/B test: #6815

This test uses the HubspotFormFromWorkPersonalToHandRaiserTestEnrollment feature flag.

• The control group sees the old signup flow, with a HubSpot form that asks if users are using Cody for work or personal
• The test group sees the new signup flow, which asks users if they'd like to learn more about Cody Enterprise

The test flow has been successful and we've decided to roll out this new flow to 100% of users.

Request
For this request, we'd like to clean up the code to standardize on using the new Cody flow.

• Please remove the code for the old Cody signup flow (the modal with the Work/Personal form)
• Please remove the feature flag (HubspotFormFromWorkPersonalToHandRaiserTestEnrollment) and event logging for that feature flag, since it will no longer be used.

As a result, all users should now see the new HubSpot modal ("Would you like to learn more about Cody Enterprise?") as they sign up.

[gitstart-app]

Here is the GitStart Ticket for this issue: https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6894

[gitstart-sourcegraph]

Hi @iskyOS
This is resolved on this PR

Thank you