Remove allocator_extension_thunks since this layer is not required

base/allocator/BUILD.gn

Index: base/allocator/BUILD.gn
diff --git a/base/allocator/BUILD.gn b/base/allocator/BUILD.gn
index ad781f8f86d685998867bf56b74bb1aefa20c134..dee067e0c15d9a068e9de6424323e6a657b2a2c6 100644
--- a/base/allocator/BUILD.gn
+++ b/base/allocator/BUILD.gn
@@ -305,15 +305,3 @@ if (use_allocator == "tcmalloc") {
     }
   }
 }  # !is_android
-
-source_set("extension_thunks") {
-  visibility = [ "//base/*" ]
-  sources = [
-    "allocator_extension_thunks.cc",
-    "allocator_extension_thunks.h",
-  ]
-  if (is_android && !is_debug) {
-    configs -= [ "//build/config/compiler:default_optimization" ]
-    configs += [ "//build/config/compiler:optimize_max" ]
-  }
-}