Only accept brotli if we can decode it

[lucaswerkmeister]

Previously, on Node versions without brotli support, axios might have arbitrarily presented the library user with a brotli-encoded response they didn’t ask for.

Resolves #5258.

[dlecan]

I have an issue with that, ie I receive br encoded data but Brotli encoding is not requested/supported.
Is it possible to merge this PR?

[DigitalBrainJS]

@dlecan Axios already contains code equivalent to this PR.

axios/lib/adapters/http.js

Lines 333 to 336 in abd2cb8

	headers.set(
	'Accept-Encoding',
	'gzip, compress, deflate' + (isBrotliSupported ? ', br' : ''), false
	);

[lucaswerkmeister]

Indeed, #5306 added slightly different code to the same effect, making this PR superfluous.