kconfig: remove unused variable in qconf.cc

If this file were compiled with -Wall, the following warning would be
reported:

scripts/kconfig/qconf.cc:312:6: warning: unused variable ‘i’ [-Wunused-variable]
  int i;
      ^

The commit prepares to turn on -Wall for C++ host programs.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

scripts/kconfig/qconf.cc

@@ -309,8 +309,6 @@ ConfigList::ConfigList(ConfigView* p, const char *name)
 	  showName(false), showRange(false), showData(false), mode(singleMode), optMode(normalOpt),
 	  rootEntry(0), headerPopup(0)
 {
-	int i;
-
 	setObjectName(name);
 	setSortingEnabled(false);
 	setRootIsDecorated(true);