Small cleanups: use `.ok()` over `match`, remove un-generated files

sdp: Use .ok() instead of match on Ok and Err

Using .ok() is more concise when loosing error context in favour of a simple None value.

Automatic replacement SSR pattern in rust-analyzer:

{let $a = $b;match $c {Ok($d) => Some($e), Err(_) => None }} ==>> {$b.ok()}

Note that rust-analyzer does not support:

• duplicate labels (ie. $c should be equal to $a, and $e equal to $d);
• statement lists yet, hence both sides are wrapped in braces.

But it performs the desired operation well enough here.

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player,webrtc: Remove flags file that is not generated anymore

Doing a clean run with all auto folders removed results in these files not being regenerated; they are empty and unreferenced from lib.rs.