Yeah, sorry about that. :-) We'll get that fixed, but in the meantime, here's a workaround you can use if you want (these instructions are for Mac, steps on Win are similar, let me know if you need me to provide them):
1. Quit Lightroom.
2. In your applications directory, right-click (control-click) on Lightroom 4.4 RC and choose "Show Package Contents".
3. Navigate to Contents/Resources/LensProfiles/1.0/Canon.
4. Select the file Canon EOS-1Ds Mark III (Canon EF 24-70mm f4L IS USM) - RAW.lcp and copy it to this directory: /Users//Library/Application Support/Adobe/CameraRaw/LensProfiles.
5. Restart Lightroom.