getent: Remove an unnecessary include statement

We do not use <features.h> anywhere, no need to include it. This makes
the Incubator compile again on FreeBSD, thus fixes #50.

Reported-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #54 from algernon/h/tfgetent-freebsd

getent: Remove an unnecessary include statement