[transport] File implementation doesn't need to inherit git::Connecti…

…on's…

…way of dealing with supported versions, but can support all. This is
because we run locally and control a git process which we assume
would hurt the caller if it was malicious.

I mean, it's nothing that's done on the server so being less
paranoid should be fine.

git-transport/src/client/blocking_io/file.rs

@@ -104,13 +104,6 @@ impl client::TransportWithoutIO for SpawnProcessOnDemand {
         self.url.to_string()
     }
 
-    fn supported_protocol_versions(&self) -> &[Protocol] {
-        self.connection
-            .as_ref()
-            .expect("this is called after the handshake")
-            .supported_protocol_versions()
-    }
-
     fn is_stateful(&self) -> bool {
         true
     }