Properly fixes#10211, wherein the config file was not being loaded
because it was considered too old. However, the modification time was
being compared against an uninitialized value; the semantics of the
uninitialized timestamp probably changed between Qt 5.4 and 5.5.
This reverts commit 60fc0af74a.
Fixes#10211. sddm fails at runtime when built with Qt 5.5. There is a
newer version of sddm which may work with Qt 5.5.
