Connectivity check should work fine with the HTTP URI; if there are
problems with that in specific environments, they need to be understood
and explained.
But more importantly, this change breaks captive portal detection, which
is one of the main purposes of connectivity check. A captive portal is
detected by NM by comparing the content returned from the connectivity
URI with a well-known content; if it's different then we assume someone
is hijacking the request (via DNS poisoning or other means). With HTTPS
this mechanism doesn't work because NM is not able to get the content
from the redirected URI due to certificate verification failure.
This reverts commit 6e53c1b52e.
