Simplify landmines code a bit now that all branches of all platforms are on ninja

BUG=none

Committed: https://crrev.com/7491d14275670fad399837445b6c1e76ff498a50
Review-Url: https://codereview.chromium.org/2071463002
Cr-Original-Commit-Position: refs/heads/master@{#408739}
Cr-Commit-Position: refs/heads/master@{#408818}
3 files changed