Loosen the 'Prefix' Check for swift:module Metadata

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The swift:module is of the form: swift:module:<Module>:<Prefix>, so it accepts two positional arguments.
If this metadata is applied to the same module within the same file (ie. you've re-opened it in the same file), we enforce that both the <Module> and <Prefix> parts are identical.

This is overzealous.
The modules do need to match, since Swift only supports having 1 module per file, but there's no reason for the prefixes to match necessarily.

We should remove this extra checking of the prefix.