[iOS][web] Change the WebView target to util

This CL changes the BUILDgn target in ios/web/web_view from web_view
to util, to reflect its current content.

Bug: none
Change-Id: I74eb4bb167b32bfc4dc4875abd6920e1d620ef9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625998
Reviewed-by: Yi Su <mrsuyi@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662613}
3 files changed