copr: Guess EPEL chroots for CentOS Stream (RhBug:2058471)

Packages built in epel-9 chroots are almost always compatible with
CentOS Stream 9.  Not having the copr plugin guess this chroot is
causing user friction.  Users are creating epel-9 chroots expecting them
to work for both CentOS Stream 9 and RHEL 9.  When they get reports
about `dnf copr enable` not working, they try to add a centos-stream-9
chroot, only to discover the dependencies they need from EPEL are not
available.

Instead of making the majority of CentOS Stream users include an
explicit chroot argument, let's reserve that workaround only for the
people that don't want their CentOS Stream systems picking the EPEL
chroot.

plugins/copr.py

@@ -469,8 +469,6 @@ def _guess_chroot(self):
                 chroot = ("opensuse-tumbleweed-{}".format(distarch))
             else:
                 chroot = ("opensuse-leap-{0}-{1}".format(dist[1], distarch))
-        elif "CentOS Stream" in dist:
-            chroot = ("centos-stream-{0}-{1}".format(dist[1], distarch))
         else:
             chroot = ("epel-%s-x86_64" % dist[1].split(".", 1)[0])
         return chroot