[MM-64630] Fix an issue where multiple channels can't be removed from policies (#32164)

* Fix an issue where multiple channels can't be removed from policies

* actually fix the issue

* use hardcoded limit

* simplify removal

server/channels/app/access_control_test.go

@@ -341,7 +341,7 @@ func TestAssignAccessControlPolicyToChannels(t *testing.T) {
 	})
 }
 
-func TestUnAssignPoliciesFromChannels(t *testing.T) {
+func TestUnassignPoliciesFromChannels(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()