Remove OatWriter::DexFileSource am: a8a815cb3a

Original change: https://android-review.googlesource.com/c/platform/art/+/2422726

Change-Id: Ie17be78625c3b5d06d835899332a38f5fe51961d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>