Drop requirement for submodules Since we don't ship bundled third-party code, these files would be missing and the builds would fail despite the fact we're linking to the system libraries.
Use system libsnappy for retracers The tracers run LD_PRELOADed into arbitrary, often closed-source binaries, so statically-link libsnappy to minimise the possibility of symbol conflicts, but the retracers don't have that constraint and are used to process untrusted data.
