virsh: maxvcpus: Always fall back to the old command if domain caps fail

1ec22be5 added code that detects the maximum cpu count according to
domain capabilities. The code fell back to the old command only if the
API was not supported. If the API fails for other reasons the command
would fail. There's no point in not trying the old API in such case.

https://bugzilla.redhat.com/show_bug.cgi?id=1402690

tools/virsh-host.c

@@ -623,9 +623,6 @@ cmdMaxvcpus(vshControl *ctl, const vshCmd *cmd)
 
         ignore_value(virXPathInt("string(./vcpu[1]/@max)", ctxt, &vcpus));
     } else {
-        if (last_error && last_error->code != VIR_ERR_NO_SUPPORT)
-            goto cleanup;
-
        vshResetLibvirtError();
     }