Remove copile time enabling of SK_ARM_HAS_NEON.

We need to know this in our build system so that we can include
the necessary neon CPP files.

R=mtklein@google.com

Review URL: https://codereview.chromium.org/432453003
diff --git a/include/core/SkPreConfig.h b/include/core/SkPreConfig.h
index 7d36891..c733111 100644
--- a/include/core/SkPreConfig.h
+++ b/include/core/SkPreConfig.h
@@ -197,10 +197,6 @@
     #define SK_CPU_ARM64
 #endif
 
-#if !defined(SK_ARM_HAS_NEON) && defined(__ARM_NEON__)
-    #define SK_ARM_HAS_NEON
-#endif
-
 //////////////////////////////////////////////////////////////////////
 
 #if !defined(SKIA_IMPLEMENTATION)