[enhancement] Remove polyfill event-source-polyfill

[mikaelol]

You are currently using the event-source-polyfill, which seems to have a bit troubled history, ref Yaffle/EventSource#202 and their current russian comment at the top of the README:

Пожалуйста не используйте эту обосранную библиотеку!

In english (google translate): Please do not use this shitty library!

EventSource is now supported by all major browsers and have been for multiple years, so I don't think the polyfill functionality is needed anymore. What makes it not trivial to just remove is that AKHQ uses the headers option of event-source-polyfill, which is not part of the official event source spec:

akhq/client/src/containers/Tail/Tail.jsx

Lines 93 to 102 in 73beccb

	this.eventSource = new EventSourcePolyfill(
	uriLiveTail(clusterId, search, selectedTopics, JSON.stringify(maxRecords)),
	localStorage.getItem('jwtToken')
	? {
	headers: {
	Authorization: 'Bearer ' + localStorage.getItem('jwtToken')
	}
	}
	: {}
	);