Disable or remap Ctrl-S which switches to HDMI

I've been struggling with Ctrl-S switching the monitor to the HDMI port at odd times. I use Ctrl-S a lot as I'm handling many files and this shortcut allows me to rename a file on saving (= Save as). Frankly, it's a damned nuisance, and I'd like to disable that action as I have no plans on using the HDMI port, and am very unlikely to have a 2nd monitor this side of 5 years, at least.

I'd appreciate any useful advice. Thanks in advance,

Paul.