Remove obsolete flag and add guard flag for AAA

We no longer use SK_ANALYTIC_AA flag it's now set as default in
Chromium. However, we need some flag to guard some bug fixes in Skia
wihtout breaking the Chromium layout tests.

BUG=

Review-Url: https://codereview.chromium.org/2536643004
Cr-Commit-Position: refs/heads/master@{#435036}

skia/config/SkUserConfig.h

@@ -228,8 +228,8 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_SUPPORT_LEGACY_IMAGE_ENCODER_CLASS
 #endif
 
-#ifndef    SK_ANALYTIC_AA
-#   define SK_ANALYTIC_AA
+#ifndef    SK_ANALYTIC_AA_GUARD
+#   define SK_ANALYTIC_AA_GUARD
 #endif
 
 ///////////////////////// Imported from BUILD.gn and skia_common.gypi