Git Repo by URL Import no longer works if the repo doesn't end in .git - Revert the original feature

Problem to solve

Per this comment, enforcing .git in the URL when importing impacted a customer in internal ticket who can no longer use Import from URL feature to import projects from xp-dev.com. It seems like there are platforms that don't necessarily expose URLs ending with .git.

Steps to reproduce

1. Create an account at xp-dev.com (they have 30 days trial with no credit card information) - > Create a test project
2. Try importing that project to GitLab using Import by URL feature.
3. Unable to find a way to get a URL ending with .git

Proposed solution

A 3-step solution was proposed in this comment:

1. Revert current MR (this issue)
2. Switch from "error message" to "warning" (#331641 (closed))
3. Switch from "warning" to a backend-based URL validation (#331805 (closed))

This issue implements step 1. The original feature should be reverted ASAP.