Don't show all elements found

This debug statement lists every element found and its dependencies on
every build; it's just noise unless you're debugging the element
dependency solver itself.  Remove from output.

Change-Id: I9281b953d958a3fd5e20edbc560a341a2fcc3deb

diskimage_builder/element_dependencies.py

@@ -103,7 +103,8 @@ class Element(object):
         self.depends = self._get_element_set(
             os.path.join(path, 'element-deps'))
 
-        logger.debug("New element : %s", str(self))
+        # Uncomment to see all elements and deps listed as they're found
+        # logger.debug("New element : %s", str(self))
 
     def __eq__(self, other):
         return self.name == other.name