Roll Fuchsia SDK from 6.20210916.2.1 to 6.20210916.3.1

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/fuchsia-sdk-chromium-autoroll
Please CC [email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Chromium: https://bugs.chromium.org/p/chromium/issues/entry

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Cq-Include-Trybots: luci.chromium.try:fuchsia-arm64-cast;luci.chromium.try:fuchsia-deterministic-dbg;luci.chromium.try:fuchsia-x64-cast
Tbr: [email protected]
Disable-Retries: true
Change-Id: I8e52f0ec88258fa87bc64f8ff5de3c5547ef1db0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3167296
Commit-Queue: chromium-autoroll <[email protected]>
Bot-Commit: chromium-autoroll <[email protected]>
Cr-Commit-Position: refs/heads/main@{#922410}

build/fuchsia/linux.sdk.sha1

@@ -1 +1 @@
-6.20210916.2.1
+6.20210916.3.1

build/fuchsia/mac.sdk.sha1

@@ -1 +1 @@
-6.20210916.2.1
+6.20210916.3.1