Remove old mingw CMake checks

This should have been removed with the code using these defines in
03ca975.

CMakeLists.txt

@@ -112,14 +112,6 @@ if(APPLE)
   add_definitions(-D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES=0)
 endif()
 
-# MinGW64 has header support but no library support for IActiveDesktop, so we
-# need to check for both the header and library and use our own implementation
-# in common/os if either doesn't exist.
-if(WIN32)
-  check_c_source_compiles("#include <windows.h>\n#include <wininet.h>\n#include <shlobj.h>\nint main(int c, char** v) {IActiveDesktop iad; (void)iad; return 0;}" HAVE_ACTIVE_DESKTOP_H)
-  check_c_source_compiles("#include <windows.h>\n#include <wininet.h>\n#include <shlobj.h>\nint main(int c, char** v) {GUID i = CLSID_ActiveDesktop; (void)i; return 0;}" HAVE_ACTIVE_DESKTOP_L)
-endif()
-
 # X11 stuff. It's in a if() so that we can say REQUIRED
 if(UNIX AND NOT APPLE)
   find_package(X11 REQUIRED)

config.h.in

@@ -1,8 +1,6 @@
 #define PACKAGE_NAME "@CMAKE_PROJECT_NAME@"
 #define PACKAGE_VERSION "@VERSION@"
 
-#cmakedefine HAVE_ACTIVE_DESKTOP_H
-#cmakedefine HAVE_ACTIVE_DESKTOP_L
 #cmakedefine ENABLE_NLS 1
 
 #cmakedefine CMAKE_INSTALL_FULL_LIBEXECDIR "@CMAKE_INSTALL_FULL_LIBEXECDIR@"