These aren't used within the verifier and no one ever extracts them.
Update-Note: Parsers for these two extensions are removed. Parsing the
types directly or passing NID_sxnet and NID_pkey_usage_period into
X509V3_get_d2i, or *_get_ext_d2i will no longer work.
Change-Id: I359e64466fd0c042eda45c41cbc0843ebb04df9f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42585
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>