How to unbind a key binding in Sublime Text 2?

{ "keys": ["ctrl+-"], "command": "noop" }

Binding a key to a no-operation or anything which wouldn't carry a command behavior, such as "hello", should work.

This would also keep the body of the binding if you change your mind in the future.

I have never see or read any official documentation about the unbound command, but it works. Another option would be removing the command attribute.

{ "keys": ["ctrl+t"] }

This will also unbound a key binding.

Also, if you're looking to undo a shortcut that was overridden by a plugin (I'm looking at you, "Terminal"):

1. find your previous shortcut in Preferences -> Key Bindings (Default)
2. Copy the line (e.g. { "keys": ["super+shift+t"], "command": "reopen_last_file" })
3. Open Preferences -> Key Bindings (User)
4. Add the the line in there (if the file is empty, it add [ and ] before the line, since it's an array of commands)

Actually this post did help me with my issue when using ST3 on mac. Using the Package Resource Viewer you can edit the default keyboard shortcuts (Default (OSX).sublime-keymap) and delete the lines that you don't want. After doing that ST3 will no longer capture your system-wide hotkeys.