Let curl select the default HTTP version (#3249)

This essentially reverts b042412416cc4ecc71c3f9c13239661a0dd588a6,
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

lib/contents.php

@@ -244,8 +244,6 @@ function _http_request(string $url, array $config = []): array
     curl_setopt($ch, CURLOPT_TIMEOUT, $config['timeout']);
     curl_setopt($ch, CURLOPT_ENCODING, '');
     curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_HTTP | CURLPROTO_HTTPS);
-    // Force HTTP 1.1 because newer versions of libcurl defaults to HTTP/2
-    curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
 
     if ($config['max_filesize']) {
         // This option inspects the Content-Length header