toolchain_utils: remove libcxxabi

BUG=b:235023022
TEST=./update_chromeos_llvm_hash_unittest.py

Change-Id: I4d015daeefff57087852c5aae0faad7d439d9267
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/3834534
Tested-by: Adrian Dole <adriandole@google.com>
Commit-Queue: Adrian Dole <adriandole@google.com>
Reviewed-by: Adrian Dole <adriandole@google.com>
Auto-Submit: Adrian Dole <adriandole@google.com>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
2 files changed