Revert "swh::deploy::worker::swh_indexer_language: Fix definition"

This reverts commit b4917f38b8aefb74352b49be59f4524c5c7bae10.

I misread the initial manifest. The language indexer inherits from the
BaseIndexer which reads the 'base.yml' configuration file. That's why
this manifest is simpler than the other indexer manifests.