STYLE: compile-type deprecate empty() method for autoPtr/tmp (#1775)

- autoPtr: less clutter using plain tests with the bool operator

    (!ptr)  vs  (ptr.empty())
    (ptr)   vs  (!ptr.empty())

- tmp: was entirely unused.

src/OpenFOAM/memory/tmp/tmpNrc.H

@@ -139,7 +139,10 @@ public:
 
     // Query
 
-        //- True if a null pointer/reference
+        //- Deprecated(2020-07) True if a null managed pointer
+        //
+        //  \deprecated(2020-07) - use bool operator
+        FOAM_DEPRECATED_FOR(2020-07, "bool operator")
         bool empty() const noexcept { return !ptr_; }
 
         //- True for non-null pointer/reference