Delete duplicate operator<< for WebSandboxFlags.

After crrev.com/c/2079621, operator<< had two different definitions in
two places. The one in sandbox_flags.h appears to be the incorrect one.

Bug: 1056945
Change-Id: I9c575492276b493e55574292ee8d385c3cdbc309
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079389Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Sajjad Mirza <sajjadm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745338}

third_party/blink/public/common/frame/sandbox_flags.h

@@ -31,10 +31,6 @@ inline constexpr WebSandboxFlags operator~(WebSandboxFlags flags) {
   return static_cast<WebSandboxFlags>(~static_cast<int>(flags));
 }
 
-inline std::ostream& operator<<(std::ostream& out, WebSandboxFlags flags) {
-  return out << std::bitset<sizeof(int) * 8>(static_cast<int>(flags));
-}
-
 }  // namespace mojom
 }  // namespace blink