Remove the PackUnpackHalfOverflow test. Different drivers handle overflow differently. The overflow case is not defined in the spec. BUG=angleproject:1044 Change-Id: I9e3883af147c6c1a4fcdcddea3ff70c62f859c56 Reviewed-on: https://chromium-review.googlesource.com/282540 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>