Rollback SwiftShader to df17a76102df.

This reverts three auto-roller commmits:
https://chromium-review.googlesource.com/c/chromium/src/+/2488154
https://chromium-review.googlesource.com/c/chromium/src/+/2487918
https://chromium-review.googlesource.com/c/chromium/src/+/2488154

Reason for rollback: Broke the Fuchsia ARM64 build (crbug.com/1140854).

TBR=chromium-autoroll@skia-public.iam.gserviceaccount.com,swiftshader-team+autoroll@google.com

Change-Id: I11c4365476e0d827e76e6ca2f7d2e8f97424152c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1140854
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_chromium_msan_rel_ng;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:linux-swangle-try-x64;luci.chromium.try:win-swangle-try-x86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490106Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819391}

DEPS

@@ -222,7 +222,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.
-  'swiftshader_revision': '84f5eeb6dd9b225f465f93737fa76aad7de355cf',
+  'swiftshader_revision': 'df17a76102dfabb3f1bd6e51449cece9f77b45e3',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.