StandardWell: pull fmt in impl file

it is not used in the interface.
no real change to the code as such, but it better reflects the use.

opm/simulators/wells/StandardWell.hpp

@@ -49,7 +49,6 @@
 
 #include <memory>
 #include <optional>
-#include <fmt/format.h>
 
 namespace Opm
 {

opm/simulators/wells/StandardWell_impl.hpp

@@ -27,6 +27,8 @@
 #include <opm/simulators/wells/WellBhpThpCalculator.hpp>
 #include <opm/simulators/wells/WellConvergence.hpp>
 
+#include <fmt/format.h>
+
 #include <algorithm>
 #include <functional>
 #include <numeric>