remove "null" value of idMethod attribute in table element

In Torque 3.3, the description of the attribute idMethod is
<!ATTLIST table
....
idMethod (idbroker|native|none|null) "null"
....
There is no reason to have the explicit value "null". As with other attributes (e.g. "default" on element column), leaving the attribute empy is more intuitive than having the string value null.

Therefore, the suggestion would be to change the definition to

idMethod (idbroker|native|none) #IMPLIED

or its xsd equivalent.