Revert "Avoid the use of P0083R3 std::set::merge"

This reverts commit 6cf4ea7.

Author: MarcoFalke

src/script/standard.cpp

@@ -366,13 +366,7 @@ void TaprootSpendData::Merge(TaprootSpendData other)
         merkle_root = other.merkle_root;
     }
     for (auto& [key, control_blocks] : other.scripts) {
-        // Once P0083R3 is supported by all our targeted platforms,
-        // this loop body can be replaced with:
-        // scripts[key].merge(std::move(control_blocks));
-        auto& target = scripts[key];
-        for (auto& control_block: control_blocks) {
-            target.insert(std::move(control_block));
-        }
+        scripts[key].merge(std::move(control_blocks));
     }
 }