rpm: always use 3 as the default python3_{pkgversion,version}

as we have the rpm macros installed in
ceph/ceph-build#1283 .

Signed-off-by: Kefu Chai <kchai@redhat.com>
(cherry picked from commit 11f0b8d)

ceph.spec.in

@@ -67,13 +67,8 @@
 
 %{!?_udevrulesdir: %global _udevrulesdir /lib/udev/rules.d}
 %{!?tmpfiles_create: %global tmpfiles_create systemd-tmpfiles --create}
-%if 0%{?rhel} == 7
-%{!?python3_pkgversion: %global python3_pkgversion 36}
-%{!?python3_version: %global python3_version 3.6}
-%else
 %{!?python3_pkgversion: %global python3_pkgversion 3}
 %{!?python3_version: %global python3_version 3}
-%endif
 # define _python_buildid macro which will expand to the empty string when
 # building with python2
 %global _python_buildid %{?_defined_if_python2_absent:%{python3_pkgversion}}