- Run dconf-editor. You can do this by opening a terminal and typing "dconf-editor" and hitting enter, or by searching for an app called "dconf Editor".
- Navigate to: org -> gnome -> desktop -> wm -> keybindings. You may see this written as "org.gnome.desktop.wm.keybindings", which means the same thing.
- Scroll through the list on the right. Any settings in bold have been changed.
- For each changed setting, click first on the setting, so that it's highlighted, and then click "Set to Default".
- Rinse, lather, repeat.
- Once you are done with that, you should also check org.gnome.settings-daemon.plugins.power, and org.gnome.settings-daemon.plugins.media-keys.
Thanks to this help page for pointing me in the correct direction!