Revert "Sovrn adapter updates: schain, digitrust, pixel syncing, and 3.0 upgrades"

[msm0504]

Reverts #4335

@aprakash-sovrn,
Your changes do not work with the latest Prebid. pixelEnabled has been deprecated.
Please merge the latest Prebid master into your fork and fix this issue before opening a new PR for these changes.

[jsnellbaker]

@aprakash-sovrn To clarify the above a bit further, the pixelEnabled field for the spec.getUserSyncs() has not been deprecated on master. It will eventually be deprecated from the public API for userSync, but even then - the structure of the syncOptions field for the spec.getUserSyncs() should remain the same.

That said - since #4335 has been merged, (at least) one of the sovrn unit tests has been consistently failing across several browsers (namely Safari, Edge, and IE).

Below is a copy of the circleci test that showed the test failures for reference:
https://circleci.com/gh/prebid/Prebid.js/4492

Can you please investigate, recreate the PR with the updates to address this issue? We're going to revert the PR for the time being.

[msm0504]

@aprakash-sovrn It's possible that using flatMap was causing the tests to fail. That function is not supported in IE, Edge, or Safari < v12.

Please try replacing that function on line 175 of your adapter. An alternative is specified at the bottom of the flatMap doc: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap

[aprakash-sovrn]

is pixel syncing being removed entirely from Prebid? or does it just need to happen in a different way now?
@msm0504 @jsnellbaker