Revert^4 "add rust_toolchain_rustc_prebuilt module type" am: f2b16069 am:...

Revert^4 "add rust_toolchain_rustc_prebuilt module type" am: f2b16069 am: 942a6409 am: b875e715 am: 511ced3a

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2761805



Change-Id: Ia40bf92a84f0a87b6863613c37ae307cb043bd54
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>