Revert "Bug 676077: Fix handling of Keyboard Input on Windows"

The actual code that does the IM context code handling on Windows now uses the
native Windows APIs to handle keystrokes, so this patch is no longer needed, as
it was found that it instead caused issues.

Pointed out in issue #2865.

This reverts commit fd6ce9975e.

gdk/gdkkeyuni.c

@@ -835,18 +835,13 @@ static const struct {
   /* Following items added to GTK, not in the xterm table */
 
   /* A few ASCII control characters */
-#ifndef GDK_WINDOWING_WIN32
+
   { 0xFF08 /* Backspace */, '\b' },
   { 0xFF09 /* Tab       */, '\t'  },
-#endif
-
   { 0xFF0A /* Linefeed  */, '\n' },
   { 0xFF0B /* Vert. Tab */, '\v' },
-
-#ifndef GDK_WINDOWING_WIN32
   { 0xFF0D /* Return    */, '\r' },
   { 0xFF1B /* Escape    */, '\033' },
-#endif
 
   /* Numeric keypad */
 
@@ -871,9 +866,7 @@ static const struct {
 
   /* End numeric keypad */
 
-#ifndef GDK_WINDOWING_WIN32
   { 0xFFFF /* Delete */, '\177' }
-#endif
 };
 
 /**