Disable macOS Catalina upgrade notice

Under macOS Mojave, the Softwareupdate control panel of System Preferences will offer the new macOS Catalina for download. As it is not necessarily useful to upgrade in the first place, the command

sudo softwareupdate --ignore "macOS Catalina"

will remove the macOS Catalina upgrade notice in System Preferences. The command

sudo softwareupdate --reset-ignored

will re-enable this.