We were using 'bb ls ... -A' which combines '-p' and '-steps', but we
only parse information from '-p'. Updates the script to only call what
it needs. Also works around current issue with '-A'.

Bug: angleproject:3429
Change-Id: I10d412885663feefd300eb135dae70b499fedd7f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1600334Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>