Revert "Device: introduce system_path() method"

This reverts commit e3e7d339bd.

src/sync_stream.rs

@@ -253,11 +253,6 @@ impl Device {
         self.raw.supported_sounds()
     }
 
-    /// Returns the system path used to open the device.
-    pub fn system_path(&self) -> &Path {
-        self.raw.system_path()
-    }
-
     /// Retrieve the current keypress state directly via kernel syscall.
     pub fn get_key_state(&self) -> io::Result<AttributeSet<Key>> {
         self.raw.get_key_state()