Remove redundant/obsolete Endpoint::reject_new_connections

This was previously used by the `quinn` layer to stop accepting
connections when the `Incoming` stream was dropped. That stream has
since been replaced by an async function. Users who still want this
can use set_server_config directly.

quinn-proto/src/endpoint.rs

@@ -709,13 +709,6 @@ impl Endpoint {
         })
     }
 
-    /// Unconditionally reject future incoming connections
-    pub fn reject_new_connections(&mut self) {
-        if let Some(config) = self.server_config.as_mut() {
-            Arc::make_mut(config).concurrent_connections(0);
-        }
-    }
-
     /// Access the configuration used by this endpoint
     pub fn config(&self) -> &EndpointConfig {
         &self.config