subtlecrypto: Don't throw exceptions twice when converting to Algorithm object

[servo-wpt-sync]

Removes match statements like

let Ok(ConversionResult::Success(algorithm)) = Algorithm::new(cx, value.handle())
else {
    return Err(Error::Syntax);
};

These don't cause issues if Algorithm::new returns Ok(ConversionResult::Failure, but in the case of Err(()) the implementation already called throw_type_error and we must not throw an additional Syntax error, otherwise we'll crash.

Luckily, this case is already handled elsewhere by the value_from_js_object macro.

Reviewed in servo/servo#34239

[wpt-pr-bot]

The review process for this patch is being conducted in the Servo project.