Unite rendering examples

[patmmccann]

Type of issue

Feature request

Description

https://github.com/prebid/Prebid.js/blob/master/integrationExamples/gpt/x-domain/creative.html and https://github.com/prebid/Prebid.js/blob/master/integrationExamples/gpt/creative_rendering.html
are prebid creatives respectively. We should publish one creative that detects it is in a safeframe and does the former logic if not, the latter if so.

[dgirardi]

Related: #9647

The cross-domain should work in both cases, and especially after that PR, there should be very little difference - and no reason to have the pbjs.renderAd example.

[patmmccann]

delete https://github.com/prebid/Prebid.js/blob/master/integrationExamples/gpt/creative_rendering.html will solve this