Rollup merge of rust-lang#75203 - canova:btreemap-into-iter, r=dtolnay

Make `IntoIterator` lifetime bounds of `&BTreeMap` match with `&HashMap`

This is a pretty small change on the lifetime bounds of `IntoIterator` implementations of both `&BTreeMap` and `&mut BTreeMap`. This is loosening the lifetime bounds, so more code should be accepted with this PR. This is lifetime bounds will still be implicit since we have `type Item = (&'a K, &'a V);` in the implementation. This change will make the HashMap and BTreeMap share the same signature, so we can share the same function/trait with both HashMap and BTreeMap in the code.

Fixes rust-lang#74034.
r? @dtolnay hey, I was touching this file on my previous PR and wanted to fix this on the way. Would you mind taking a look at this, or redirecting it if you are busy?

Author: Manishearth

alloc/src/collections/btree/map.rs

@@ -1294,7 +1294,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, K: 'a, V: 'a> IntoIterator for &'a BTreeMap<K, V> {
+impl<'a, K, V> IntoIterator for &'a BTreeMap<K, V> {
     type Item = (&'a K, &'a V);
     type IntoIter = Iter<'a, K, V>;
 
@@ -1363,7 +1363,7 @@ impl<K, V> Clone for Iter<'_, K, V> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, K: 'a, V: 'a> IntoIterator for &'a mut BTreeMap<K, V> {
+impl<'a, K, V> IntoIterator for &'a mut BTreeMap<K, V> {
     type Item = (&'a K, &'a mut V);
     type IntoIter = IterMut<'a, K, V>;