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 am: 8afa4301

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



Change-Id: I8b51c2d9e7af30ab1ff0605367efe780343c1450
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>