Remove unnecessary rust_ffi entries

The build system no longer allows defining rust_ffi_rlibs in
static_libs for rust modules.

libbt_shim_ffi isn't needed as libbt_shim is already included in
rustlibs.

libbluetooth_core_rs is not needed as libbluetooth_core_rs_facade is
included in rustlibs.

Bug: 254469782
Test: m rust
Test: mma
Change-Id: I513b0446216c5417906b886d1ac8d7b8896cc235