partially revert 'Added features that allow the reader to accept common non-standard JSON.'

revert '642befc836ac5093b528e7d8b4fd66b66735a98c',
but keep the *added* methods for `decodedNumber()` and `decodedDouble()`.

include/json/features.h

@@ -44,12 +44,6 @@ public:
   /// \c true if root must be either an array or an object value. Default: \c
   /// false.
   bool strictRoot_;
-
-  /// \c true if dropped null placeholders are allowed. Default: \c false.
-  bool allowDroppedNullPlaceholders_;
-
-  /// \c true if numeric object key are allowed. Default: \c false.
-  bool allowNumericKeys_;
 };
 
 } // namespace Json