Remove sync user agent product in build.py

Building with "ChromeWebView" doesn't actually work so it I'll just
remove it.

Bug: 941313
Change-Id: Id4602116417281c5ef9c25a7aa06848b5f9b3489
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1838450Reviewed-by: Hiroshi Ichikawa <ichikawa@chromium.org>
Commit-Queue: John Wu <jzw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703587}

ios/web_view/tools/build.py

@@ -223,9 +223,6 @@ def main():
     extra_gn_options += 'ios_web_view_include_cronet=false '
   if options.enable_sync:
     extra_gn_options += 'ios_web_view_enable_sync=true '
-    # Used to differentiate //ios/web_view from //ios/chrome in the user agent
-    # product string passed to sync servers.
-    extra_gn_options += 'sync_user_agent_product="ChromeWebView" '
   else:
     extra_gn_options += 'ios_web_view_enable_sync=false '
   if options.enable_autofill: