ENH: unify use of dictionary method names

- previously introduced `getOrDefault` as a dictionary _get_ method,
  now complete the transition and use it everywhere instead of
  `lookupOrDefault`. This avoids mixed usage of the two methods that
  are identical in behaviour, makes for shorter names, and promotes
  the distinction between "lookup" access (ie, return a token stream,
  locate and return an entry) and "get" access (ie, the above with
  conversion to concrete types such as scalar, label etc).

src/functionObjects/utilities/setTimeStep/setTimeStepFunctionObject.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2013-2016 OpenFOAM Foundation
-    Copyright (C) 2016-2019 OpenCFD Ltd.
+    Copyright (C) 2016-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -95,7 +95,7 @@ bool Foam::functionObjects::setTimeStepFunctionObject::read
     timeStepPtr_ = Function1<scalar>::New("deltaT", dict);
 
     // Ensure that adjustTimeStep is active
-    if (!time_.controlDict().lookupOrDefault<bool>("adjustTimeStep", false))
+    if (!time_.controlDict().getOrDefault("adjustTimeStep", false))
     {
         FatalIOErrorInFunction(dict)
             << "Need to set 'adjustTimeStep' true to allow timestep control"