Since util.gyp doesn't have any executables, there isn't any need to
include it from all.gyp.  It should only be included by targets that
depend upon it.

BUG=angle:761

Change-Id: Iabad2da7bca0f161d092c044ab0021568f9b6f59
Reviewed-on: https://chromium-review.googlesource.com/219759Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>