XML support is removed from Xero API Integrations

Xero seems to have less and less support or documentation for application/xml or text/xml response types even if XML is the default response type.

XML support will be removed to simplify the code and testing of Xero API module.

This only affects contributed or custom modules that use the XeroQuery::setFormat method or manually set the Accept or Content-Type headers when querying the Xero API. Every Typed Data data type behavior should be seamless with the exceptions of any data bugs that already exist.

Before

      $accounts = $this->query
        ->setType('xero_account')
        ->setFormat('xml')
        ->setMethod('get')
        ->execute();

After

      $accounts = $this->query
        ->setType('xero_account')
        ->setMethod('get')
        ->execute();