Remove legacy stdlib source path am: a16023dd72

Original change: https://android-review.googlesource.com/c/platform/prebuilts/rust/+/3469939

Change-Id: I7a8c13b2e6e870687ceaaa5ab8bd74d5914ef507
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>