rust: Remove stack-depth sancov

This flag causes a linkage error between rustc and our libclang_rt. We
can remove it for now and look into reintroducing it in the future.

We'd need to define 'thread_local uintptr_t __sancov_lowest_stack' to
support this. See https://reviews.llvm.org/D36839

Bug: 180495975
Test: m <fuzzer>
Change-Id: I95c9392307b5f20a0eda0fc76eb7ef79e27ae4df