STYLE: can use bool instead of Switch version of dictionary::lookupOrDefault

- both versions handle the same input words.
  Only need the <Switch> version when the destination variable is
  also a Switch and we need to output the word later.

src/OpenFOAM/matrices/solution/solution.H

@@ -36,7 +36,6 @@ SourceFiles
 #define solution_H
 
 #include "IOdictionary.H"
-#include "Switch.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -57,7 +56,7 @@ class solution
         dictionary cache_;
 
         //- Switch for the caching mechanism
-        Switch caching_;
+        bool caching_;
 
         //- Dictionary of relaxation factors for all the fields
         dictionary relaxationFactors_;