Remove recruiting email from onboarding series

What does this MR do and why?

• removes the onboarding experience survey email and the survey results landing page with the calendly_invite_link feature flag that is contained in it
• reasons to remove it #360822 (comment 959983490) and further clarification in #360822 (comment 1025198179)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #360822 (closed)