systemvm: remove logrotate config for wtmp and btmp

logrotate in systemvms run every day. it exits with failure.
```
root@r-100-VM:~# systemctl status logrotate
● logrotate.service - Rotate log files
   Loaded: loaded (/lib/systemd/system/logrotate.service; static; vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2021-03-23 00:00:01 UTC; 2 days ago
     Docs: man:logrotate(8)
           man:logrotate.conf(5)
  Process: 25001 ExecStart=/usr/sbin/logrotate /etc/logrotate.conf (code=exited, status=1/FAILURE)
 Main PID: 25001 (code=exited, status=1/FAILURE)

Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.
```

it is because the logrotate for wtmp and btmp already exist in 4.15 systemvm template.
```
root@r-100-VM:~# cat /etc/logrotate.d/wtmp
/var/log/wtmp {
    missingok
    monthly
    create 0664 root utmp
    minsize 1M
    rotate 1
}
root@r-100-VM:~# cat /etc/logrotate.d/btmp
/var/log/btmp {
    missingok
    monthly
    create 0660 root utmp
    rotate 1
}
```

remove them from /etc/logrotate.conf fixes the issue.
```
root@r-100-VM:~# systemctl status logrotate
● logrotate.service - Rotate log files
   Loaded: loaded (/lib/systemd/system/logrotate.service; static; vendor preset: enabled)
   Active: inactive (dead) since Thu 2021-03-25 00:00:01 UTC; 9h ago
     Docs: man:logrotate(8)
           man:logrotate.conf(5)
  Process: 28211 ExecStart=/usr/sbin/logrotate /etc/logrotate.conf (code=exited, status=0/SUCCESS)
 Main PID: 28211 (code=exited, status=0/SUCCESS)

Mar 25 00:00:01 r-100-VM systemd[1]: Starting Rotate log files...
Mar 25 00:00:01 r-100-VM systemd[1]: logrotate.service: Succeeded.
Mar 25 00:00:01 r-100-VM systemd[1]: Started Rotate log files.
```

Author: ustcweizhou

systemvm/debian/etc/logrotate.conf

@@ -11,15 +11,3 @@ size 50M
 compress
 # RPM packages drop log rotation information into this directory
 include /etc/logrotate.d
-# no packages own wtmp and btmp -- we'll rotate them here
-/var/log/wtmp {
-    monthly
-    create 0664 root utmp
-    rotate 1
-}
-/var/log/btmp {
-    missingok
-    monthly
-    create 0600 root utmp
-    rotate 1
-}

systemvm/debian/etc/logrotate.d/btmp

@@ -0,0 +1,7 @@
+# no packages own btmp -- we'll rotate it here
+/var/log/btmp {
+    missingok
+    monthly
+    create 0660 root utmp
+    rotate 1
+}

systemvm/debian/etc/logrotate.d/wtmp

@@ -0,0 +1,8 @@
+# no packages own wtmp -- we'll rotate it here
+/var/log/wtmp {
+    missingok
+    monthly
+    create 0664 root utmp
+    minsize 1M
+    rotate 1
+}