Update github org membership requirements

Membership across orgs is now equivalent. When joining a Kubernetes
GitHub Org, you are now joining the Kubernetes project and have
implicit membership in the other active orgs.

ref: kubernetes/org#966

community-membership.md

@@ -50,12 +50,7 @@ remain active contributors to the community.
 - Sponsored by 2 reviewers. **Note the following requirements for sponsors**:
     - Sponsors must have close interactions with the prospective member - e.g. code/design/proposal review, coordinating
       on issues, etc.
-    - Sponsors must be reviewers or approvers in at least 1 OWNERS file either in any repo in the [Kubernetes org],
-    or the org they are sponsoring for.
-      - An approver/reviewer in the [Kubernetes org] may sponsor someone for the [Kubernetes org]
-      or any of the related [Kubernetes GitHub organizations]; as long as it's a project they're involved with.
-      - A sponsor who is an approver/reviewer in any of the related [Kubernetes GitHub organizations]
-      but not in the [Kubernetes org] can only sponsor someone for the orgs they are associated with.
+    - Sponsors must be reviewers or approvers in at least one OWNERS file within one of the [Kubernetes GitHub organizations].
     - Sponsors must be from multiple member companies to demonstrate integration across community.
 - **[Open an issue][membership request] against the kubernetes/org repo**
    - Ensure your sponsors are @mentioned on the issue
@@ -69,14 +64,11 @@ remain active contributors to the community.
 There are related [Kubernetes GitHub organizations], such as [kubernetes-sigs].
 We are currently working on automation that would transfer membership in the
 Kubernetes organization to any related orgs automatically, but such is not the
-case currently. If you are a Kubernetes org member, you are implicitly eligible
-for membership in related orgs, and can request membership when it becomes
-relevant, by creating a PR directly or [opening an issue][membership request]
+case currently. If you are a member of one of these Orgs, you are implicitly
+eligible for membership in related orgs, and can request membership when it
+becomes relevant, by creating a PR directly or [opening an issue][membership request]
 against the kubernetes/org repo, as above.
 
-However, if you are a member of any of the related
-[Kubernetes GitHub organizations] but not of the [Kubernetes org],
-you will need explicit sponsorship for your membership request.
 
 ### Responsibilities and privileges