Expose wlr-data-control-unstable-v1 to non-sandboxed clients

Some users have complained about not supporting clipboard managers. But
this was possible, but hidden under the `COSMIC_DATA_CONTROL_ENABLED`
env var.

Since the security context protocol exists now to provide a way to not
expose a protocol like this to sandboxed clients, it should be safe to
expose this now.

src/wayland/handlers/data_control.rs

@@ -8,7 +8,7 @@ use smithay::{
 
 impl DataControlHandler for State {
     fn data_control_state(&mut self) -> &mut DataControlState {
-        self.common.data_control_state.as_mut().unwrap()
+        &mut self.common.data_control_state
     }
 }