[depends] Don't build shared libs in native protobuf

Summary: The native protobuf build has been migrated to support cmake (which is available with the new protobuf versions) but the configuration option for disabling the shared libraries has not been ported over and still uses the previous syntax.

Test Plan: Run the gitian builds.

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13470