Fix a bug introduced by 2ca153141 (I merged the wrong patchset).
Issue happens when pipeline is split by phases into independent
evals (e.g. build/release/deploy).
Splitting extra steps requires knowledge of all known phases,
otherwise pipeline evaluation fails due to extra steps from inactive
phases.
Change-Id: Iab0f2dc3eadda281e483055e26f00a95442e15b0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6942
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>