lib/model: Remove superfluous check for IndexID in remote ClusterConfig (#5717)

The check in ClusterConfig() when iterating through announced devices
in a folder explicitly skips entries without a non-zero IndexID.
Therefore, the check for IndexID == 0 just below will never be true
and the intended cleanup of local index data will not happen.

Plainly remove that check to make the intended case distinction work.
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