Remove unused C #includes in headers

Don't include standard C headers that aren't even used for anything by the
wx headers.

Author: lanurmi

include/wx/datetime.h

@@ -19,8 +19,6 @@
 
 #include <vector>
 
-#include <limits.h>             // for INT_MIN
-
 #include "wx/longlong.h"
 #include "wx/anystr.h"
 

include/wx/strconv.h

@@ -15,8 +15,6 @@
 #include "wx/chartype.h"
 #include "wx/buffer.h"
 
-#include <stdlib.h>
-
 class WXDLLIMPEXP_FWD_BASE wxString;
 
 // the error value returned by wxMBConv methods

include/wx/stream.h

@@ -14,7 +14,6 @@
 
 #if wxUSE_STREAMS
 
-#include <stdio.h>
 #include "wx/object.h"
 #include "wx/string.h"
 #include "wx/filefn.h"  // for wxFileOffset, wxInvalidOffset and wxSeekMode

include/wx/string.h

@@ -26,11 +26,7 @@
     #include <ctype.h>
 #endif
 
-#include <string.h>
-#include <stdio.h>
 #include <stdarg.h>
-#include <limits.h>
-#include <stdlib.h>
 
 #include "wx/chartype.h"    // for wxChar
 #include "wx/wxcrtbase.h"   // for wxChar, wxStrlen() etc.

include/wx/utils.h

@@ -48,8 +48,6 @@ class WXDLLIMPEXP_FWD_BASE wxArrayInt;
     #include <unistd.h>
 #endif
 
-#include <stdio.h>
-
 #include <unordered_map>
 
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