extension: Remove duplicate calls to getOptions

[kjarosh]

This hopefully will improve loading time.

[danielhjacobs]

Would this be equivalent (same for enableSWFTakeover)?

async function enable(opt?: Options) {

[danielhjacobs]

This works fine and I don't see a downside and it makes sense, but in testing it seems like the speed difference is negligible.

For testing, I built Ruffle with this commit and Ruffle without this commit (checking out the prior commit), and added some logging.

Namely, in both versions I added this to the start:

let startTime: number | null = null;

Added this inside the if in the IIFE:

startTime = performance.now();

And added this in the if (options.ruffleEnable)/if (ruffleEnable) in enableSWFTakeover:

            if (startTime !== null) {
                const elapsed = performance.now() - startTime;
                console.log(`[Perf] enableSWFTakeover reached ruffleEnable check in ${elapsed.toFixed(2)} ms`);
            }

Loading both into Chromium where header conditions are supported, I opened "service worker" in chrome://extensions/ for Ruffle. In the console log for background.js, the time it took to progress through those functions was within the margin of error between the two (toggling the extension on and then off then reopening the service worker log serves to give another data point, and what I mean is the time it took for one was between the min and max time it could take for the other).