glib: Use std::hint::black_box() instead of criterion version of it

Author: sdroege

glib/benches/gstring.rs

@@ -1,5 +1,6 @@
-use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use criterion::{criterion_group, criterion_main, Criterion};
 use glib::IntoGStr;
+use std::hint::black_box;
 
 pub fn str_into_gstr(c: &mut Criterion) {
     c.bench_function("str as IntoGStr", |b| {