Let unix Squeak VM generate ASCII control characters like it always did

Note: I have reverted my deeper changes that did always used the `KeySym *symbolic`as event `charCode`.
This will be for another branch and will require coordinated cross platform support and image changes.
This makes Nuke-MacRoman branch a good candidate for fixing #456
...at least for ctrl+a to ctrl+z

platforms/unix/vm-display-X11/sqUnixX11.c

@@ -1955,6 +1955,7 @@ static int x2sqKeyPlain(XKeyEvent *xevt, KeySym *symbolic)
       return -1;	/* unknown key */
   if ((charCode == 127) && mapDelBs)
     charCode= 8;
+#ifdef PharoVM
   if (charCode >= 1 && charCode <= 26) {
     /* check for Ctrl-letter that gets translated into charCode 1-26 instead of letters a-z */
     KeySym keysym = *symbolic;
@@ -1963,6 +1964,7 @@ static int x2sqKeyPlain(XKeyEvent *xevt, KeySym *symbolic)
     if (keysym >= XK_A && keysym <= XK_Z)
       return (int)'A' + (keysym - XK_A);
   }
+#endif
   return charCode;
 }