core/manager: drop obsolete cgroup taint string

Wwe can't boot on systems without cgroup anyway
(even cgroup v1 will be gone pretty soon).

catalog/systemd.catalog.in

@@ -558,8 +558,6 @@ Defined-By: systemd
 Support: %SUPPORT_URL%
 
 The following "tags" are possible:
-- "cgroups-missing" — the kernel was compiled without cgroup support or access
-  to expected interface files is restricted
 - "var-run-bad" — /var/run is not a symlink to /run
 - "overflowuid-not-65534" — the kernel user ID used for "unknown" users (with
   NFS or user namespaces) is not 65534

man/org.freedesktop.systemd1.xml

@@ -1668,14 +1668,6 @@ node /org/freedesktop/systemd1 {
 
         </varlistentry>
 
-        <varlistentry>
-          <term><literal>cgroups-missing</literal></term>
-
-          <listitem><para>Support for cgroups is unavailable.</para>
-
-          <xi:include href="version-info.xml" xpointer="v252"/></listitem>
-        </varlistentry>
-
         <varlistentry>
           <term><literal>cgroupsv1</literal></term>
 

src/core/manager.c

@@ -4836,22 +4836,19 @@ static int short_uid_range(const char *path) {
 }
 
 char* manager_taint_string(const Manager *m) {
+        const char *stage[11] = {};
+        size_t n = 0;
+
         /* Returns a "taint string", e.g. "local-hwclock:var-run-bad". Only things that are detected at
          * runtime should be tagged here. For stuff that is known during compilation, emit a warning in the
          * configuration phase. */
 
         assert(m);
 
-        const char* stage[12] = {};
-        size_t n = 0;
-
         _cleanup_free_ char *usrbin = NULL;
         if (readlink_malloc("/bin", &usrbin) < 0 || !PATH_IN_SET(usrbin, "usr/bin", "/usr/bin"))
                 stage[n++] = "unmerged-usr";
 
-        if (access("/proc/cgroups", F_OK) < 0)
-                stage[n++] = "cgroups-missing";
-
         if (cg_all_unified() == 0)
                 stage[n++] = "cgroupsv1";