[WPT] Fix WPT tools rolling script to consider symlinks.

Bug: 1163537
Change-Id: Ibf607274909ddc7435f45dc55a005c5d4f14ff15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2613148Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841463}

third_party/blink/tools/blinkpy/third_party/wpt/checkout.sh

@@ -27,7 +27,7 @@ function reduce {
   # xargs on some platforms, so we remove those directories first.
   rm -fr html css
   # Remove all except white-listed.
-  comm -23 <(find . -type f | sort) <(cat ../WPTIncludeList | sort) | xargs -d '\n' -n 1 rm
+  comm -23 <(find . -type f -o -type l | sort) <(cat ../WPTIncludeList | sort) | xargs -d '\n' -n 1 rm
   find . -empty -type d -delete
 }