Revert "Fix notification icon not appearing in Unity"

This fixes builds currently failing at runtime with this D-Bus error:
  arguments to dbus_message_iter_append_basic() were incorrect,
  assertion "_dbus_check_is_valid_path (*string_p)" failed in file
  dbus-message.c line 2680.

This reverts commit 3939820389d995f56a073fc1d54ab245c6558312.

Unfixes bug #1269