This story will remove the vendored copy of BoringSSL from the bssl-compat layer, and replace it by using the copy of BoringSSL that is already fetched by envoy's bazel build system, as a regular bazel dependency. This will ensure that we always track the version used by envoy.

Note that we currently have some S390x/PPC fixes that have been made directly as edits to the compatibility layer's vendored copy of BoringSSL. Those fixes will need rewriting as patches to be applied to the BoringSSL dependency when bazel fetches it.