collab: Remove Stripe code (#36275)

This PR removes the code for integrating with Stripe from Collab.

All of these concerns are now handled by Cloud.

Release Notes:

- N/A

crates/collab/src/db/tables/billing_subscription.rs

@@ -1,5 +1,4 @@
 use crate::db::{BillingCustomerId, BillingSubscriptionId};
-use crate::stripe_client;
 use chrono::{Datelike as _, NaiveDate, Utc};
 use sea_orm::entity::prelude::*;
 use serde::Serialize;
@@ -160,17 +159,3 @@ pub enum StripeCancellationReason {
     #[sea_orm(string_value = "payment_failed")]
     PaymentFailed,
 }
-
-impl From<stripe_client::StripeCancellationDetailsReason> for StripeCancellationReason {
-    fn from(value: stripe_client::StripeCancellationDetailsReason) -> Self {
-        match value {
-            stripe_client::StripeCancellationDetailsReason::CancellationRequested => {
-                Self::CancellationRequested
-            }
-            stripe_client::StripeCancellationDetailsReason::PaymentDisputed => {
-                Self::PaymentDisputed
-            }
-            stripe_client::StripeCancellationDetailsReason::PaymentFailed => Self::PaymentFailed,
-        }
-    }
-}