CMake: remove dict.c form hiredis_sources

[Lipraxde]

Commit c6b8bd7 to make all functions in dict.c static. If a CMake project set warning unused functions, and include hiredis using add_subdirectory , this cause warnings / errors.

[bjosv]

Nice to get CMake and make builds more alike, even that dict is not part of the external symbols (nm -g) nor included in the installed headers.
Building hiredis itself with something like -Wall today will also trigger the warnings you mentioned.