How to disable or remove the YaraScanService (MRT.app)?
As mentioned in this article YaraScanService is part of the MRT.app (Malware Removal Tool). If you are sure your system is not infected with malware and you don't want Apple to do automatic malware protection for you without asking your consent, then you can disable and/or remove the MRT service using these commands:

sudo launchctl stop com.apple.mrt
sudo launchctl remove com.apple.mrt


The corresponding .plist files are apparently located at:

/System/Library/LaunchDaemons/com.apple.MRTd.plist
/System/Library/LaunchAgents/com.apple.MRTa.plist


If the above method does not work for you (apparently the daemon can re-enable itself), then a more radical approach would be to disable SIP with csrutil disable from recovery mode, and remove executable permissions on the MRT and YaraScanService files with:

chmod -R -x+X /System/Library/CoreServices/MRT.app


Once you have changed the permissions it is recommended to re-enable SIP again with csrutil enable (from recovery mode).