clean up SK_SUPPORT_LEGACY_A8_MASKBLITTER

cannot find anyone defining it

Change-Id: Ia93555b4d8fa1c07dd932dc39fe8854518f1455e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/207720
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/core/SkBlitter_ARGB32.cpp b/src/core/SkBlitter_ARGB32.cpp
index abd63b7..88a8fdf 100644
--- a/src/core/SkBlitter_ARGB32.cpp
+++ b/src/core/SkBlitter_ARGB32.cpp
@@ -1155,35 +1155,18 @@
 static void blend_row_A8(SkPMColor* dst, const void* vmask, const SkPMColor* src, int n) {
     auto mask = (const uint8_t*)vmask;
 
-#ifdef SK_SUPPORT_LEGACY_A8_MASKBLITTER
-    for (int i = 0; i < n; ++i) {
-        if (mask[i]) {
-            dst[i] = SkBlendARGB32(src[i], dst[i], mask[i]);
-        }
-    }
-#else
     Sk4px::MapDstSrcAlpha(n, dst, src, mask, [](const Sk4px& d, const Sk4px& s, const Sk4px& aa) {
         const auto s_aa = s.approxMulDiv255(aa);
         return s_aa + d.approxMulDiv255(s_aa.alphas().inv());
     });
-#endif
 }
 
 static void blend_row_A8_opaque(SkPMColor* dst, const void* vmask, const SkPMColor* src, int n) {
     auto mask = (const uint8_t*)vmask;
 
-#ifdef SK_SUPPORT_LEGACY_A8_MASKBLITTER
-    for (int i = 0; i < n; ++i) {
-        if (int m = mask[i]) {
-            m += (m >> 7);
-            dst[i] = SkAlphaMulQ(src[i], m) + SkAlphaMulQ(dst[i], 256 - m);
-        }
-    }
-#else
     Sk4px::MapDstSrcAlpha(n, dst, src, mask, [](const Sk4px& d, const Sk4px& s, const Sk4px& aa) {
         return (s * aa + d * aa.inv()).div255();
     });
-#endif
 }
 
 static void blend_row_lcd16(SkPMColor* dst, const void* vmask, const SkPMColor* src, int n) {