This cleans up the remnants of ArrayAccessorExpression which was renamed
in a838bb718.
Change-Id: Ie2c67a49e63774d8b153ec17c3185652708a91e5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/68942
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>