don't test index8 -- no longer supported

Bug: skia:6828
Change-Id: I7ce4d91c2fa66b3a81e5143819dd9d774fa1c116
Reviewed-on: https://skia-review.googlesource.com/23140
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>

tests/ImageIsOpaqueTest.cpp

@@ -61,6 +61,11 @@ DEF_TEST(ImageInfo_flattening, reporter) {
     };
 
     for (int ct = 0; ct <= kLastEnum_SkColorType; ++ct) {
+#ifdef SK_SUPPORT_LEGACY_INDEX_8_COLORTYPE
+        if (ct == kIndex_8_SkColorType) {
+            continue;
+        }
+#endif
         for (int at = 0; at <= kLastEnum_SkAlphaType; ++at) {
             for (auto& cs : spaces) {
                 SkImageInfo info = SkImageInfo::Make(100, 200,