Remove Digitrust Support

[SyntaxNode]

This issue is forked from an effort started by @patmmccann to begin removing Digitrust support since the IAB is no longer supporting it. The IAB issues a PR recently to remove support from PrebidJS: prebid/Prebid.js#5334

Proposal

• Remove all explicit support for Digitrust from code, including all tests.
• Remove the ext definition of Digitrust from the user.ext data structure.
• Leave adapters which specifically look for Digitrust alone.

Open Questions

• Some adapters are using the user.ext data structure to avoid code deduplication. Should we perhaps then leave the data structure alone and add a comment that's deprecated?
• Should we still remove it when enforcing privacy policies (GDPR, CCPA, COPPA, ...)?

References In Code To Digitrust

• endpoints/amp_auction_test.go : has additional tests that include digitrust.
• endpoints/auction.go : validateUser() has some validation around digitrust.
• endpoints/openrtb2/sample-requests/valid-whole/digitrust.json : exists should be renamed and edited if it is otherwise a useful test, or removed.
• exchange/exchange_test.go : a couple of tests reference digitrust, we should perhaps remove the digitrust part of the sample requests.
• exchange/utils_test.go : a couple of tests reference digitrust, we should perhaps remove the digitrust part of the sample requests.
• exchange/utils.go : extractBuyerUIDs() is digitrust aware. We may want to excise that code.
• exchange/exchangetest/request-other-user-ext.json : Modify or remove test?
• exchange/exchangetest/request-user-no-prebid.json : Modify or remove test?
• openrtb_ext/user.go : We have the digitrust spec defined in the user.ext definitions.
• privacy/scrubber.go : We have code handling digitrust.
• privacy/scrubber_test.go : We have tests covering digitrust.

[SyntaxNode]

Work is still needed for both PBS-Go and PBS-Java. The linked PR is not the complete solution for PBS-Go.

[SyntaxNode]

Implemented in PBS-Go 0.166.0.

[bretg]

Done with PBS-Java 1.52