comctl32/tests: Remove dead assignment in comboex.c (Cppcheck)

[Bruno Jesus]

[dlls\comctl32\tests\comboex.c:130] ->
[dlls\comctl32\tests\comboex.c:146]: (performance) Variable 'res' is
reassigned a value before the old one has been used.
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diff --git a/dlls/comctl32/tests/comboex.c b/dlls/comctl32/tests/comboex.c
index af01839..faa32a3 100644
--- a/dlls/comctl32/tests/comboex.c
+++ b/dlls/comctl32/tests/comboex.c
@@ -127,7 +127,7 @@ static HWND subclass_editbox(HWND hwndComboEx)
 
 static void test_comboboxex(void) {
     HWND myHwnd = 0;
-    LONG res = -1;
+    LONG res;
     COMBOBOXEXITEMA cbexItem;
     static const char *first_item  = "First Item",
                 *second_item = "Second Item",