collab: Remove unused RateLimiter (#29343)

This PR removes the `RateLimiter` from the collab codebase, as it is no
longer used.

Release Notes:

- N/A

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

@@ -1,31 +0,0 @@
-use crate::db::UserId;
-use sea_orm::entity::prelude::*;
-
-#[derive(Clone, Debug, PartialEq, Eq, DeriveEntityModel)]
-#[sea_orm(table_name = "rate_buckets")]
-pub struct Model {
-    #[sea_orm(primary_key, auto_increment = false)]
-    pub user_id: UserId,
-    #[sea_orm(primary_key, auto_increment = false)]
-    pub rate_limit_name: String,
-    pub token_count: i32,
-    pub last_refill: DateTime,
-}
-
-#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
-pub enum Relation {
-    #[sea_orm(
-        belongs_to = "super::user::Entity",
-        from = "Column::UserId",
-        to = "super::user::Column::Id"
-    )]
-    User,
-}
-
-impl Related<super::user::Entity> for Entity {
-    fn to() -> RelationDef {
-        Relation::User.def()
-    }
-}
-
-impl ActiveModelBehavior for ActiveModel {}