I'm currently upgrading my wikis from 1.34.4 to 1.35.1, pulling the source directly from the REL1_35 branch on GitHub. When I run the invalidateUserSessions.php maintenance script from the new version, it works but throws the warning indicated by the header:

PHP Warning: curl_multi_setopt(): CURLPIPE_HTTP1 is no longer supported in /PATH/TO/includes/libs/http/MultiHttpClient.php on line 455

Apparently the integer constant for the value rather than the named constant was used in the code, so a code search of the constant name turned up no results.
https://github.com/wikimedia/mediawiki/blob/REL1_35/includes/libs/http/MultiHttpClient.php#L455