configure.ac: readd missing test on "modern" utmp database

There was an incompatible change in struct utmp and the test to validate
if we are using the old or the new format has been removed in the
past decade somehow.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
fixup! configure.ac: readd missing test on "modern" utmp database
affile: test_affile_open added