IWYU: Update for Debian 12 CI job

`include-what-you-use` diagnostics, in practice, are specific to
the environment's compiler and standard library.  Update includes
to satisfy IWYU for our CI job under Debian 12.

Source/cmExportBuildAndroidMKGenerator.h

@@ -8,7 +8,6 @@
 #include <string>
 
 #include "cmExportBuildFileGenerator.h"
-#include "cmExportFileGenerator.h"
 #include "cmStateTypes.h"
 
 class cmGeneratorTarget;