Stop passing %{release} to meson when building in upstream mode

When building in upstream mode, the release doesn't really have any
meaning so let's stop passing it as part of the version-tag and
shared-library-tag arguments.

This also makes it possible to make the release a timestamp so that
each package built from upstream is guaranteed to be newer. If we
pass the release to meson via version-tag and shared-library-tag and
the release changes every build, we end up having constant rebuilds
of various targets in meson that depend on the version.

systemd.spec

@@ -661,9 +661,9 @@ CONFIGURE_OPTS=(
         -Dsplit-bin=true
         -Db_ndebug=false
         -Dman=enabled
-        -Dversion-tag=%{version}-%{release}
+        -Dversion-tag=%{version}%[%{without upstream}?"-%{release}":""]
         # https://bugzilla.redhat.com/show_bug.cgi?id=1906010
-        -Dshared-lib-tag=%{version_no_tilde}-%{release}
+        -Dshared-lib-tag=%{version_no_tilde}%[%{without upstream}?"-%{release}":""]
         -Dfallback-hostname="localhost"
         -Ddefault-dnssec=no
         -Ddefault-dns-over-tls=no