Revert "Add missing reference to index"

This reverts commit 54a4fd76.

docs/devel/api-reference.rst

@@ -18,7 +18,6 @@ by components:
    swh.auth <swh-auth/index>
    swh.core <swh-core/index>
    swh.counters <swh-counters/index>
-   swh.datasets <swh-datasets/index>
    swh.deposit <swh-deposit/index>
    swh.export <swh-export/index>
    swh.fuse <swh-fuse/index>