CMakeLists.txt: remove obsolete WX_SOURCE support

Author: smanders

build/CMakeLists.txt

@@ -30,16 +30,9 @@ set(plot_hdrs
   )
 list(APPEND ${lib_name}_libsrcs ${plot_hdrs})
 #######################################
-if(DEFINED WX_SOURCE)
-  message(STATUS "WX_SOURCE: ${WX_SOURCE}") # passed-in via externpro
-endif()
-#######################################
 add_library(${lib_name} STATIC ${${lib_name}_libsrcs})
 target_include_directories(${lib_name} PUBLIC $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../include>
-  PRIVATE
-  # wxplotctrl plotdraw.cpp needs to include wx/gtk/dcclient.h when building against gtk2
-  ${WX_SOURCE}/include # TODO should be removed when building against gtk2 becomes obsolete
   )
 target_link_libraries(${lib_name} PUBLIC things)
 list(TRANSFORM WXX_OUTPUT_NAME REPLACE "@TARGET@" "${lib_name}")