This essentially reverts b042412416,
as YouTube seems to have fixed their servers.
At least I was able to query the YouTube endpoint around 150 times with
CURL_HTTP_VERSION_2TLS recently. They even advertise HTTP/3 support with
an `alt-svc` HTTP header now.
This unsets CURLOPT_HTTP_VERSION to let curl decide
on the version. This would support all curl versions and opens the
possibility for HTTP/3, but leads to inconsistent behavior depending
on the underlying curl version.
We don't set CURL_HTTP_VERSION_NONE explicitly, as it is always the curl
default and opens the path to let individual bridges override the HTTP
version where necessary.
Alternatively, setting CURL_HTTP_VERSION_2TLS explicitly would lead to consistent behavior
regardless of the curl version, but might uncover old curl bugs before the
developers enabled HTTP/2 by default.
Additionally, that requires at least PHP 7.0.7 (we require PHP 7.4
already) and curl 7.47.0 [1], released on Jan 27 2016 [2].
See also the discussion on https://github.com/RSS-Bridge/rss-bridge/pull/3249
[1] https://www.php.net/manual/curl.constants.php
[2] https://curl.se/docs/releases.html
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