Remove not existing table fields in PDU table

[cxhong]

For issue #4739

Remove not existing attributes for pdu table. machine type, model number and serial number. Those information can get from rinv command.

The current attributes for PDU table are:

# tabdump pdu
#node,nodetype,pdutype,outlet,username,password,snmpversion,community,snmpuser,authtype,authkey,privtype,privkey,seclevel,comments,disable

[xcatbot]

CI CHECK RESULT : > PR FORMAT CORRECT> BUILD SUCCESSFUL > INSTALL XCAT SUCCESSFUL> CODE SYNTAX CORRECT> FAST REGRESSION TEST Successful: Totalcase 215 Pass 215 failed 0

[immarvin]

agree to merge