hg-core: use anonymous lifetime for `impl Chunk` (D8958#inline-15003 followup)

Differential Revision: https://phab.mercurial-scm.org/D9103

rust/hg-core/src/revlog/patch.rs

@@ -17,7 +17,7 b" struct Chunk<'a> {"
     data: &'a [u8],
 }
 
-impl<'a> Chunk<'a> {
+impl Chunk<'_> {
     /// Adjusted start of the chunk to replace.
     ///
     /// Offset allow to take into account the growth/shrinkage of data