Don't include sanitizers GN file on Mac

This is a Chromium specific file that's not present in Fuchsia.

Change-Id: I926d166617ab10cdf2fd8050353ad3f422626312
diff --git a/BUILD.gn b/BUILD.gn
index 14d986a..916121b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -9,10 +9,6 @@
   import("//build/config/android/rules.gni")
 }
 
-if (is_mac) {
-  import("//build/config/sanitizers/sanitizers.gni")
-}
-
 # Meta target that includes both icuuc and icui18n. Most targets want both.
 # You can depend on the individually if you need to.
 group("icu") {