sub_store: Remove role field and SubscriptionRole type.

This commit removes role field from StreamSubscription
type and also removes SubscriptionRole type since we are
not moving forward with stream administrator concept and
instead working on new permssions model as per #19525.

static/js/sub_store.ts

@@ -7,11 +7,6 @@ export const enum StreamPostPolicy {
     MODERATORS = 4,
 }
 
-export const enum SubscriptionRole {
-    STREAM_ADMINISTRATOR = 20,
-    MEMBER = 50,
-}
-
 export type Stream = {
     date_created: number;
     description: string;
@@ -37,7 +32,6 @@ export type StreamSubscription = Stream & {
     is_muted: boolean;
     pin_to_top: boolean;
     push_notifications: boolean | null;
-    role: SubscriptionRole;
     stream_weekly_traffic: number | null;
     subscribers?: number[];
     wildcard_mentions_notify: boolean | null;