d/steamvr_lh: Make sure the context is release on exit

Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2229>

src/xrt/drivers/steamvr_lh/steamvr_lh.cpp

@@ -734,6 +734,7 @@ void
 destroy(struct xrt_system_devices *xsysd)
 {
 	u_system_devices_close(xsysd);
+	svrs->ctx.reset();
 	free(svrs);
 }