"http://fedoraproject.org/static/hotspot.txt gives "OK" even with location services switched off in privacy ?
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that location service is not related to NetworkManager connectivity checking
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location service is used by weather application for example, possibly clocks ... to determine your location
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not Captive Portal on/off ?
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no there is no easy on/off switch, it is still a hard dependency as package, but you can for example create a same config file in /etc/NetworkManager/conf.d/99-connectivity-fedora.conf for example with "blank" uri "uri=" and "interval=0" that will override the default 20-connectivity-fedora.conf (man 5 NetworkManager.conf CONECTIVITY SECTION ... )
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here is a upstream bug report about making the easy "on/off" option available (or some other solution) https://bugzilla.gnome.org/show_bug.cgi?id=737362
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also that URL will always return OK if it is "real" so no MITM, its content wont change in any way when local settings are changed, it is only used with known content and accessed over secure connection to verify you have access to the internet ... (in case of MITM, it will fail, because certificate for fp.o cannot be valid assuming CAs don't allow someone to create one for that domain ... and they "sign it") "