[boringssl] Remove shanyu from OWNERS.

I am leaving the team, remove my name from OWNERS.

Change-Id: I64b9fd702d81a75847e642fc28dc4e890f5a294b
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/boringssl/+/536201
Fuchsia-Auto-Submit: Yu Shan <shanyu@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Reviewed-by: Aaron Green <aarongreen@google.com>