Replace base string utils with android::base ones am: 0c18424d12

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3320834

Change-Id: I84714623efde427958dd83e3e4b166e222f69101
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>