Remove member_access from project policy

What does this MR do and why?

Follow up to Enable Guest+ users to execute custom agents in... (!214918 - merged)

After conversing with the Authz team we realized that introducing yet another permission (member_access) could add more confusion to engineers and refactoring project policy to not enable guest_access for non-members when public is the actual fix we want.

This MR is the compromise that we found before doing the larger refactor while still keeping our codebase reasonable.

• call project.member? directly
• remove redundant enabled permissions

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