Remove useless wx/wx.h include, that create sometimes compil warnings on msys.

wx/wx.h includes all wxWidgets .h files, and sometimes creates collision
names in #define between kicad and windows headers
Moreover, blindly including a lot of useless files is compil time consuming

eeschema/sheet.cpp

@@ -28,7 +28,6 @@
 #include <project.h>
 #include <wildcards_and_files_ext.h>
 #include <tool/tool_manager.h>
-#include <wx/clipbrd.h>
 #include <sch_edit_frame.h>
 #include <sch_plugins/legacy/sch_legacy_plugin.h>
 #include <sch_sheet.h>
@@ -40,6 +39,9 @@
 #include <dialogs/dialog_sheet_properties.h>
 #include <tool/actions.h>
 
+#include <wx/clipbrd.h>
+#include <wx/dcmemory.h>
+
 
 bool SCH_EDIT_FRAME::CheckSheetForRecursion( SCH_SHEET* aSheet, SCH_SHEET_PATH* aHierarchy )
 {