Fix the review of the checks-wait milestone: redeliveries, deleted modules, the kept queue

A check pending redelivery is read before the let-through fetches (none is handed back);
a deleted module is done for the plan's key; the queue an ask came from is let go of when
it ends. Tries say they run under their own id.

cmd/mesh-controller/plans_building.go

@@ -42,7 +42,7 @@ func buildPhaseOf(p inventory.Plan) bool {
 			if st != nil && st.State != "" {
 				asked = true
 			}
-			if st == nil || st.State != "built" {
+			if st == nil || (st.State != "built" && st.State != planDeleted) {
 				unbuilt = true
 			}
 		}

cmd/mesh-controller/plans_building_test.go

@@ -81,6 +81,8 @@ func TestAPlanIsInItsBuildPhaseFromTheFirstAskToTheLastBuild(t *testing.T) {
 		{"between two tiers", aPlan("p", inventory.PlanRolling, tiers, map[string]string{"a": "built", "b": "built"}), true},
 		{"the last tier asked", aPlan("p", inventory.PlanBuilding, tiers, map[string]string{"a": "built", "b": "built", "c": "asked"}), true},
 		{"every build built", aPlan("p", inventory.PlanRolling, tiers, map[string]string{"a": "built", "b": "built", "c": "built"}), false},
+		// A module the plan deletes is done as far as its tiers go (release_plan.go), so it holds no key through the rollout.
+		{"a deleted module is done", aPlan("p", inventory.PlanRolling, tiers, map[string]string{"a": "built", "b": "built", "c": planDeleted}), false},
 		{"failed", aPlan("p", inventory.PlanFailed, tiers, map[string]string{"a": "failed", "b": "asked"}), false},
 		{"superseded", aPlan("p", inventory.PlanSuperseded, tiers, map[string]string{"a": "asked"}), false},
 		{"a batch whose window is open", aPlan("p", inventory.PlanAssembling, tiers, map[string]string{"a": "asked"}), false},