misc: remove readfile function.

readfile() function was only used inside its own tests, and due to
recent changes of file-system type detection being removed, it began
reading always reading with O_DIRECT.

Its tests do not pass on F20 since they do not read an aligned block
size, but since nothing uses this code but the tests itself we can
simply remove it.

Change-Id: I1dd05b8d4533277dc4f0eaf408ac533cd09e0585
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27959
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>