Revert "check Ruby strings for embedded null bytes"

This reverts commit 29dfda0011.
It turned out to be a bad idea after all.

binding-mri/binding-util.cpp

@@ -191,7 +191,7 @@ rb_get_args(int argc, VALUE *argv, const char *format, ...)
 			if (!RB_TYPE_P(tmp, RUBY_T_STRING))
 				rb_raise(rb_eTypeError, "Argument %d: Expected string", argI);
 
-			*s = StringValueCStr(tmp);
+			*s = RSTRING_PTR(tmp);
 			++argI;
 
 			break;

binding-mri/bitmap-binding.cpp

@@ -32,7 +32,7 @@ DEF_TYPE(Bitmap);
 static const char *objAsStringPtr(VALUE obj)
 {
 	VALUE str = rb_obj_as_string(obj);
-	return StringValueCStr(str);
+	return RSTRING_PTR(str);
 }
 
 void bitmapInitProps(Bitmap *b, VALUE self)