fix: remove dead PSI forwarding listener memory leak

[patrickhulce]

AFAICT this code is not used. The metric values are pulled from storage in the popup and nothing I could find listened for the event that was being issued.

On top of that, this chunk of code adds a listener every time a metric update event is issued :)

Repro Steps

1. Open a clean browser profile.
2. Inspect background page and open Memory + Performance Monitor panels.
3. Reset the extension at chrome://extensions and then open 5 tabs of https://melodic-class.glitch.me/cls-forever.html
4. Hold down Ctrl+Tab for 60 seconds.

Before

After

[addyosmani]

Thank you for digging in here, @patrickhulce! 🤛

On top of that, this chunk of code adds a listener every time a metric update event is issued :)

Removing this forwarding listener certainly makes sense until we land #53.

I may be missing a step, but after following the steps outlined above, I was able to reproduce the memory issues but was not able to see the drop in memory comparing this PR to master.

Could you check if there's a step missing from the above to get that nice "after" view? :) I'm also happy to retest this using a particular Chrome channel you're testing against (using ToT atm)

[patrickhulce]

but was not able to see the drop in memory comparing this PR to master

Were you observing memory usage using the method described in #71 or this PR?

There's a separate issue that causes needless cycling of memory (#73) but not really leak on the same level as this.

[addyosmani]

There's a separate issue that causes needless cycling of memory (#73) but not really leak on the same level as this.

Ack! Thanks for clarifying. I circled back and used the approach you outlined with the Memory panel again to verify this patch reduced memory and there is a verifiable reduction.

Thanks once again for discovering this leak, @patrickhulce!