encoding/json/v2: remove `unknown` tag option and DiscardUnknownMembers

WARNING: This commit contains breaking changes
for those already using GOEXPERIMENT=jsonv2.

This removes support for the `unknown` tag option and
the DiscardUnknownMembers marshal option.

The `unknown` tag option semantics are a bit too subtle
even for experienced Go programmers to understand.
Remove support for it. The exact same feature (or something similar)
can be added back into a future release of json/v2.

We already support the `inline` tag option,
which can handle most cases of what someone might want to do
with unknown fields (such as preserve them).

Fixes #77271
Updates #76444

Change-Id: I875952f0755e58aac4c571869b2cdb56e75cfda9
Reviewed-on: https://go-review.googlesource.com/c/go/+/741320
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

0 files changed, 0 insertions, 0 deletions