Fix cross joins in epics_finder

What does this MR do and why?

Fixes cross joins in epics_finder by removing the line that allows cross joins across databases.

Part of the Cells: Fix all the cross joins between users an... (&10973 - closed) epic where we are tracking fixing of all cross joins between users and namespaces.

Related to: #419221 (closed)

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #419221 (closed)