Revert "Reland "Do not create 4-byte sequences in `ConvertUtf16ToModifiedUtf8()`"" am: a0dcfaf559 am: f48971200b

Original change: https://android-review.googlesource.com/c/platform/art/+/2377248

Change-Id: I820d657dc07d0e301320ae276b84d50fccc92e6d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>