Investigate why the presubmit did not catch missing files

https://github.com/bazel-contrib/bazel-docs/commit/01462d226e477325b6fbe7f207bfc98bac23ef9b added a lot of files to the navigation, including three that no longer exist.

For some reason the presubmit check succeeded (https://buildkite.com/bazel/bazel-books-bazel-docs/builds/420#01a047a1-ca2d-4e07-9650-a65c2f91e2ce), even though a later check in a different pipeline failed as expected: https://buildkite.com/bazel/google-bazel-presubmit/builds/108073#01a047b0-1c18-47fc-bdae-9d8f004f3a35

Both pipelines use the same presubmit code, so the different behavior is odd.

Update: I've removed the files in https://github.com/bazel-contrib/bazel-docs/pull/698 and https://github.com/bazel-contrib/bazel-docs/pull/700.

Start by comparing the presubmit implementation and configuration used by the bazel-books-bazel-docs and google-bazel-presubmit Buildkite runs linked in the issue. Inspect the referenced commit and the logs for build 420 and build 108073 to identify why missing navigation files were handled differently. Done means explaining the discrepancy and correcting the presubmit behavior or documenting the required fix; the files were removed in PRs 698 and 700.

Written by the indexing model from the issue text.