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

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

Change-Id: Ic8c8e62e0af075b98e946339989f569872ac8f33
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>