Drop 'support-cors' usersync YAML config

[bretg]

Since before even my time in PBS, the YAML files have supported a 'support-cors' field in usersync. Of 230+ bid adapters, only 2 set this to true.

I don't see any code in PBS that looks at this field.

My suspicion is that it's an information flag indicating that the bidder's sync endpoint sets some specific CORS header like Access-Control-Allow-Credentials and/or Access-Control-Allow-Origin. However, That's not documented anywhere and I'm not aware of the use case that drive this ancient config setting.

So I'm proposing that we either:

• drop support-cors from the usersync YAML entirely
• OR document what use case it supports and when bidders should declare support-cors:true