Playground XYZ adapter - iframe usersync bug fix

[monofonik]

Type of change

• Bugfix
• Feature
• New bidder adapter
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Does this change affect user-facing APIs or examples documented on http://prebid.org?
• Other

Description of change

• Fixes a bug where "image" type user sync pixels are not being dropped when the publisher allows iframe usersync.
• Removes a redundant iframe sync pixel URL from the Playground XYZ adapter code.

[bretg]

please add a unit test confirming that the adapter responds with an image regardless of syncOptions

[monofonik]

Thanks @bretg PR updated. Noticed the CircleCI build is failing - but doesn't appear to be an issue with my changes?

[bretg]

Thanks - looks good. CircleCI has been kinda flaky lately. Re-running.

[bretg]

@monofonik - please resync this PR with master. I'm told that may eliminate the circleci problem. I've re-run this several times to no avail.

[monofonik]

Thanks @bretg updated looks good now

[bretg]

Merged. While I have your attention here, would like to pick up or close out prebid/prebid.github.io#1203

[monofonik]

Thanks @bretg I'll reply on the other PR