Remove keyboard layout from OS X leaving custom layouts only

I have multiple nonstandard input sources that fully replace the original keyboard layout OS X ships with. However, the remove button is grayed out for the only original layout I would like to remove. It's obviously meant for preventing users from losing keyboard input if their custom layouts are not working.

Can I remove the layout manually from some config plist, leaving only the last three?

(In fact, it would suffice to remove the language from input select rotation.)

Solution 1:

1. Change the current input source to a custom keyboard layout.
2. Open ~/Library/Preferences/com.apple.HIToolbox.plist (in 10.9) or ~/Library/Preferences/ByHost/com.apple.HIToolbox.*.plist (in 10.8 and earlier). You can convert the plist to XML with plutil -convert xml1.
3. Remove the input source or input sources you want to disable from the AppleEnabledInputSources dictionary. If there is an AppleDefaultAsciiInputSource key, remove it.
4. Restart.

See https://apple.stackexchange.com/questions/44921/how-to-remove-or-disable-a-default-keyboard-layout for more information.