Remove unused and bad isPrintable(Expression) function

Fixes #1361

Author: mgreter

src/util.cpp

@@ -582,10 +582,6 @@ namespace Sass {
       return true;
     }
 
-    bool isPrintable(Expression* e, Output_Style style) {
-      return isPrintable(e, style);
-    }
-
     bool isPrintable(Supports_Block* f, Output_Style style) {
       if (f == NULL) {
         return false;

src/util.hpp

@@ -46,7 +46,6 @@ namespace Sass {
     bool isPrintable(String_Constant* s, Output_Style style = NESTED);
     bool isPrintable(String_Quoted* s, Output_Style style = NESTED);
     bool isPrintable(Declaration* d, Output_Style style = NESTED);
-    bool isPrintable(Expression* e, Output_Style style = NESTED);
     bool isAscii(const char chr);
 
   }