enable unused_self lint

Functions using `services()` are allowed to pointlessly take `self`
because the existence of `services()` is a crime and the solution is
making the types store references to their dependencies and then going
through `self`, so just allowing the lint saves us from modifying some
code only to switch it back later. Much later. Getting rid of
`services()` will probably be an ordeal.

src/service/rooms/state_compressor.rs

@@ -89,6 +89,8 @@ impl Service {
         }
     }
 
+    // Allowed because this function uses `services()`
+    #[allow(clippy::unused_self)]
     pub(crate) fn compress_state_event(
         &self,
         shortstatekey: u64,
@@ -106,6 +108,8 @@ impl Service {
     }
 
     /// Returns shortstatekey, event id
+    // Allowed because this function uses `services()`
+    #[allow(clippy::unused_self)]
     pub(crate) fn parse_compressed_state_event(
         &self,
         compressed_event: &CompressedStateEvent,