Remove unnecessary compiler allow

bindgen no longer emits the troublesome code that required the allow.

Signed-off-by: mulhern <[email protected]>

devicemapper-rs-sys/src/lib.rs

@@ -1,6 +1,5 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
-#![allow(deref_nullptr)]
 #![allow(clippy::all)]
 
 include!(concat!(env!("OUT_DIR"), "/dm-bindings.rs"));