Revert^2 "add rust_toolchain_rustc_prebuilt module type" am: 9333ac12 am:...

Revert^2 "add rust_toolchain_rustc_prebuilt module type" am: 9333ac12 am: c640053d am: 8de7c130 am: d2505229

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2746466



Change-Id: I9aa82674220945ebcd2853574bca8c152207042d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>