Remove unused NULL_POINTER_ERROR constant from error.rs

Author: sameerank

datadog-ffe-ffi/src/error.rs

@@ -3,8 +3,6 @@
 
 use ddcommon_ffi::Error;
 
-const NULL_POINTER_ERROR: &str = "null pointer provided";
-
 pub fn ffe_error(msg: &str) -> Error {
     Error::from(msg)
 }