Fixed more compile time errors

src/service/rooms/metadata/data.rs

@@ -1,4 +1,5 @@
 use ruma::RoomId;
+use crate::Result;
 
 pub trait Data {
     fn exists(&self, room_id: &RoomId) -> Result<bool>;

src/service/rooms/metadata/mod.rs

@@ -2,13 +2,13 @@ mod data;
 pub use data::Data;
 use ruma::RoomId;
 
-use crate::service::*;
+use crate::Result;
 
 pub struct Service<D: Data> {
     db: D,
 }
 
-impl Service<_> {
+impl<D: Data> Service<D> {
     /// Checks if a room exists.
     #[tracing::instrument(skip(self))]
     pub fn exists(&self, room_id: &RoomId) -> Result<bool> {