systemd: Update to 199

This incorporates some changes from
https://github.com/vcunat/nixpkgs/commit/eb64a2f5620a9ba6ac7f598694d82db0cf83e669.
Delete all kernels older than 2.6.39

Systemd doesn't support those kernels, so there is no point in keeping
them around.
Linux kernel: Enable CONFIG_FHANDLE

This enables the open_by_handle_at(2) and name_to_handle_at(2)
syscalls.  Systemd kind of requires this.
man-pages: Update to 3.50
systemd: Enable the firmware loader in udev

It's needed in kernels < 3.8.