External users are initially invited to create a project

Context: !64268 (comment 604516706)

When impersonating (or logging in as) an external user, I notice they are invited to create a project in the landing page. However, external users can't create a new project so it's strange UX.

Proposal

• Remove the project creation card.

Implementation plan

• Remove else statement in app/views/dashboard/projects/_blank_state_welcome.html.haml#L13