STYLE: can add compile-time deprecated message for autoPtr::set()

- deprecated Feb-2018, but not marked as such.

  The set() method originally enforce an additional run-time check
  (Fatal if pointer was already set), but this was rarely used.
  In fact, the set() method was invariably used in constructors
  where the pointer by definition was unset.

  Can now mark as deprecated to catch the last of these.
  We prefer reset() for similarity with std::unique_ptr

  Eg,
  FOAM_EXTRA_CXXFLAGS="-DFoam_autoPtr_deprecate_setMethod"  wmake

src/phaseSystemModels/multiphaseInter/phasesSystem/phaseModel/PurePhaseModel/PurePhaseModel.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017 OpenCFD Ltd.
+    Copyright (C) 2017-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -28,6 +28,7 @@ License
 #include "PurePhaseModel.H"
 #include "phaseSystem.H"
 #include "basicThermo.H"
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class BasePhaseModel, class phaseThermo>
@@ -39,14 +40,14 @@ Foam::PurePhaseModel<BasePhaseModel, phaseThermo>::PurePhaseModel
 :
     BasePhaseModel(fluid, phaseName)
 {
-    thermoPtr_.set
+    thermoPtr_.reset
     (
         phaseThermo::New
         (
             fluid.mesh(),
             phaseName,
             basicThermo::phasePropertyName(basicThermo::dictName, phaseName)
-        ).ptr()
+        )
     );
 
 }