Remove redundant headers from the build system

Headers are not to be placed amongst the source files in the CMake
script. The preprocessor and the linker will take care of glue all the
files together. Also, the "include_directories()" statement at the top
of the file already tells CMake where to look for all the needed
header files.

src/cli/CMakeLists.txt

@@ -15,31 +15,18 @@
 
 set(cli_SOURCES
         Add.cpp
-        Add.h
         Clip.cpp
-        Clip.h
         Command.cpp
-        Command.h
         Diceware.cpp
-        Diceware.h
         Edit.cpp
-        Edit.h
         Estimate.cpp
-        Estimate.h
         Extract.cpp
-        Extract.h
         Generate.cpp
-        Generate.h
         List.cpp
-        List.h
         Locate.cpp
-        Locate.h
         Merge.cpp
-        Merge.h
         Remove.cpp
-        Remove.h
-        Show.cpp
-        Show.h)
+        Show.cpp)
 
 add_library(cli STATIC ${cli_SOURCES})
 target_link_libraries(cli Qt5::Core Qt5::Widgets)