[CMake] Removing configurations.

[Josef Karthauser]

> I can add a configuration by using following the instructions here:
> 
> 
>
http://www.cmake.org/Wiki/CMake_FAQ#How_can_I_extend_the_build_modes_wit
h_a_custom_made_one_.3F
> 
> How do I go about removing an existing one?

Answering my own question, I now see I don't need to.  Instead I just
define the configurations I'm interested in using the
CMAKE_CONFIGURATION_TYPES variable.

Joe