There is not a direct Group Policy setting that disables IE. There are three ways that I can think of to disable it from functioning to connect to the Internet.
The first is using the IE policies. This method breaks IE, but does not prohibit it from running. This solution configures the Proxy Settings incorrectly. Give it a Proxy server name or address that does not exist, or a wrong port to use for the proxy. You can configure this setting under User Configuration|Windows Settings|Internet Explorer Maintenance|Connection|Proxy Settings. IE will look for a Proxy server, but always fail.
The other two ways target the IE application directly. First, you can configure the Don't Run Specified Windows Applications policy, which is located under User Configuration|Administrative Templates|System. Just add in Iexplore.exe to deny IE from running. The second way is to use a Software Restriction policy for Iexplore.exe. You could use a path rule here, but I would suggest using a hash rule, to ensure the file can't be moved or renamed.