Remove generic flags for stdlibs from BUILD file am: ba0d00462e am: ca86110367 am: cbfd9717c3 am: 24cc306d17

Original change: https://android-review.googlesource.com/c/platform/prebuilts/rust/+/2777189

Change-Id: I0b6eed50481d42354916b53982fe6aa0b91cf559
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>