cpp-btree: Remove trivial operator!= no longer required in C++20

src/3rdparty/cpp-btree/btree.h

@@ -796,11 +796,8 @@ struct btree_iterator {
   }
   void decrement_slow();
 
-  bool operator==(const const_iterator &x) const {
-    return node == x.node && position == x.position;
-  }
-  bool operator!=(const const_iterator &x) const {
-    return node != x.node || position != x.position;
+  friend bool operator==(const btree_iterator &a, const btree_iterator &b) noexcept {
+    return a.node == b.node && a.position == b.position;
   }
 
   // Accessors for the key/value the iterator is pointing at.

src/3rdparty/cpp-btree/btree_container.h

@@ -133,10 +133,6 @@ class btree_container {
     return true;
   }
 
-  bool operator!=(const self_type& other) const {
-    return !operator==(other);
-  }
-
   // Functor retrieval
   key_compare key_comp() const { return tree_.key_comp(); }
 

src/3rdparty/cpp-btree/safe_btree.h

@@ -116,11 +116,8 @@ class safe_btree_iterator {
   }
 
   // Equality/inequality operators.
-  bool operator==(const const_iterator &x) const {
-    return iter() == x.iter();
-  }
-  bool operator!=(const const_iterator &x) const {
-    return iter() != x.iter();
+  friend bool operator==(const safe_btree_iterator &a, const safe_btree_iterator &b) noexcept {
+    return a.iter() == b.iter();
   }
 
   // Accessors for the key/value the iterator is pointing at.