Roll src/third_party/libavif/src/ f88383daa..616bd4f9a (4 commits)

https://chromium.googlesource.com/external/github.com/AOMediaCodec/libavif.git/+log/f88383daa8de..616bd4f9aeca

$ git log f88383daa..616bd4f9a --date=short --no-merges --format='%ad %ae %s'
2020-09-03 wtc Remove 16bpc cases in avifLimitedToFullY(), etc.
2020-09-03 wtc Remove the avifCodecSpecificOptionsGet() function
2020-09-01 wtc Add the libaom-specific option tune=METRIC
2020-09-01 wtc Make avifCodecSpecificOptionsGet a const function

Created with:
  roll-dep src/third_party/libavif/src
R=dalecurtis@chromium.org

Change-Id: Ia50e27556d10ac03221d1c950bcaa510614e65f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2398964Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Cr-Commit-Position: refs/heads/master@{#805039}

DEPS

@@ -342,7 +342,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling libavif
   # and whatever else without interference from each other.
-  'libavif_revision': 'f88383daa8de92d57e898cce9c2d23a9fe87802c',
+  'libavif_revision': '616bd4f9aecaa38c1e1f83b4f79fd6df5d4b1467',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling nearby
   # and whatever else without interference from each other.