Use slices.DeleteFunc to remove chains with invalid policies and
incompatible key usage, instead of iterating over the chains and
reconstructing the slice.
Change-Id: I8ad2bc1ac2469d0d18b2c090e3d4f702b1b577cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/708415
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Daniel McCarney <daniel@binaryparadox.net> Reviewed-by: David Chase <drchase@google.com>