[minigraph.py]: Remove members list from VLAN, it is not supported in YANG models.

[praveen-li]

- What I did
Remove members list from VLAN, it is not supported in YANG models.

minigraph.py generates config_db json data from minigraph, today it also
generates vlan['members'] field which is invalid as per YANG models.
This PR removes VLAN['members'] from json format.

Related Command: sonic-cfggen -H -m /etc/sonic/minigraph.xml --print-data

- How I did it
Let vlan['members'] get filled in parse_dpg(), but remove it from json before assignment in result in function parse_xml().

- How to verify it
Before Fix:

sonic-cfggen -H -m /etc/sonic/minigraph.xml --print-data | grep -A 20 VLAN
–
"VLAN": {
  "Vlan1000": {
      "vlanid": "1000",
      "dhcp_servers": [ "192.0.0.1", "192.0.0.2", "192.0.0.3", "192.0.0.4" ],
      "members": [
        "Ethernet4",
        "Ethernet8",
        "Ethernet12",
–

After Fix:
sonic-cfggen -H -m /etc/sonic/minigraph.xml --print-data | grep -A 20 VLAN

--
"VLAN": {
  "Vlan1000": { 
     "vlanid": "1000", 
     "dhcp_servers": [ "192.0.0.1", "192.0.0.2", "192.0.0.3", "192.0.0.4" ] 
   }
},

- Description for the changelog

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