Disable a Sublime key-binding entirely?

Edit: if you want to prevent Sublime from capturing the keyboard shortcut completely, instead of just getting Sublime to do nothing when you use the shortcut, see J Spen's answer below.

Owen_R's solution does not work in Sublime 3; instead of false, just put a command that does not exist:

{ "keys": ["ctrl+up"],          "command": "pass" },
{ "keys": ["ctrl+down"],        "command": "pass" },
{ "keys": ["ctrl+shift+up"],    "command": "pass" },
{ "keys": ["ctrl+shift+down"],  "command": "pass" },

I know this post is old and you asked specifically for ST2, but since this post still appears in the first results on most search engines, I think it will help people to find ST3's solution here too.

If you want to bind something like ctrl+l to other things using ctrl+l w for example then disabling it won't work because will completely disable the use of ctrl+l for complex bindings as well. You have to install package: PackageResourceViewer and then using the command palette in sublime after installing use open Resource from that package and navigate to Default/Default (Your OS).sublime-keymap. Then comment out the lines in this file of the bindings you don't want. This won't override them but just permanently remove them as defaults so other packages can set and use them so depends your desired outcome.

Oh, it's just:

{ "keys": ["ctrl+up"],          "command": false },
{ "keys": ["ctrl+down"],        "command": false },
{ "keys": ["ctrl+shift+up"],    "command": false },
{ "keys": ["ctrl+shift+down"],  "command": false },