Update policy to reference emails_enabled instead of emails_disabled

#24733 (closed) is working on removing usages of emails_disabled and I think the policy should be updated for projects and groups (to cause less confusion when emails_disabled is deprecated for both)

The following discussion from !121585 (merged) should be addressed:

• @terrichu started a discussion: (+3 comments)

  question (non-blocking): is there an issue to update this policy? I don't think it needs to be part of this and can be in a follow up