Remove stale usage of doc(cfg)

tcharding · tcharding · commit c3450f391326 · 2023-05-24T22:02:24.000+10:00
We no longer need to use `doc(cfg())` because we use `doc_cfg_auto`,
remove it.
diff --git a/bitcoin/src/blockdata/script/push_bytes.rs b/bitcoin/src/blockdata/script/push_bytes.rs
@@ -106,7 +106,6 @@ mod primitive {
         RangeToInclusive<usize>
     );
     #[cfg(feature = "rust_v_1_53")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "rust_v_1_53")))]
     delegate_index!((Bound<usize>, Bound<usize>));
 
     impl Index<usize> for PushBytes {
