ENH: construct string types from Istream now explicit (#1033)

- this helps for trapping unguarded dictionary lookups.

src/OpenFOAM/primitives/strings/parsing/parsing.H

@@ -49,8 +49,6 @@ namespace Foam
 
 namespace parsing
 {
-  // Enumerations
-
     //- Enumeration for possible parsing error
     enum class errorType
     {