[DO NOT MERGE] Remove unused LLVM prebuilts am: ecc94a1d1e am: 477be6baab

Original change: https://googleplex-android-review.googlesource.com/c/platform/prebuilts/clang/host/darwin-x86/+/18131640

Change-Id: I842449d2fc5690740cd2fcfc3e0c527d6dac0160
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>