subunit is required on centos as well as fedora

Remove fedora dependency restriction on subunit and subunit-devel packages.
libsunit is only called in test/ext/Makefile on all platforms safe opensuse.

Change-Id: I483f42f20f6ba8bd112c18a9c51753a5d816d1c1
Signed-off-by: Gabriel Ganne <gabriel.ganne@enea.com>
Signed-off-by: Romain Ly <romain.ly@enea.com>

extras/rpm/vpp.spec

@@ -32,9 +32,7 @@ Release: %{_release}
 Requires: vpp-lib = %{_version}-%{_release}, net-tools, pciutils, python
 BuildRequires: systemd, chrpath
 BuildRequires: check, check-devel
-%if  0%{?fedora} >= 25
 BuildRequires: subunit, subunit-devel
-%endif
 %if 0%{?fedora} >= 26
 BuildRequires: compat-openssl10-devel
 BuildRequires: python2-devel, python2-virtualenv