Update github importer PAT text for ci_cd_only projects

What does this MR do?

This MR updates GitHub importer Personal Access Token text for ci_cd_only projects. Because of recent changes importing of ci cd projects using OAuth has been removed (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30716 & https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31488), leaving only PAT token import as an option. I am removing text saying Alternatively, you can use a %{personal_access_token_link}. since this is the only option now.

Screenshots

Please see text under PAT input field.

Before

After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Performance and Testing

N/A

Security

N/A