Investigate whether try/catch statement is necessary when building list of target hosts for /make_* endpoints

[matrixbot]

This issue has been migrated from #8808.

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The do_invite_join, do_remotely_reject_invite and (if matrix-org/synapse#6739 is merged) do_knock all include a similar bit of code for inserting a remote server name at the beginning of a list of target hosts. This code includes a try/catch statement for ValueError that seems unnecessary.

https://github.com/matrix-org/synapse/blob/7127855741faaf9544339db4faa7d25b0158fdfc/synapse/handlers/federation.py#L1360-L1367

https://github.com/matrix-org/synapse/blob/b08dc7effed4a880384e386cdca50c5d15870904/synapse/handlers/federation.py#L1655-L1662