coinselection: Remove COutput operators == and !=

These operators are used only by the tests in std::mismatch. As
std::mismatch can take a binary predicate, we can use a lambda that
achieves the same instead.

src/wallet/coinselection.h

@@ -84,14 +84,6 @@ public:
     bool operator<(const COutput& rhs) const {
         return outpoint < rhs.outpoint;
     }
-
-    bool operator!=(const COutput& rhs) const {
-        return outpoint != rhs.outpoint;
-    }
-
-    bool operator==(const COutput& rhs) const {
-        return outpoint == rhs.outpoint;
-    }
 };
 
 /** Parameters for one iteration of Coin Selection. */