remove unused local typedef

Fixes this warning from g++ 4.8:

CMake/Source/cmDocumentation.cxx:835:23: warning: typedef 'sdoc_t' locally defined but not used [-Wunused-local-typedefs]
         SDOC_UNKNOWN} sdoc_t;
                       ^
Merge topic 'remove-local-typedef' into next

2a7fecc remove unused local typedef