SigninManagerBase doesn't need a weak pointer

After https://codereview.chromium.org/14630003, there are no uses of
SigninManagerBase's weak pointer.

Change-Id: I3ed342d5434d40ee63be3a4ae8cf785e49fb21da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1642553Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#665885}

components/signin/core/browser/signin_manager_base.cc

@@ -34,8 +34,7 @@ SigninManagerBase::SigninManagerBase(
       token_service_(token_service),
       account_tracker_service_(account_tracker_service),
       initialized_(false),
-      account_consistency_(account_consistency),
-      weak_pointer_factory_(this) {
+      account_consistency_(account_consistency) {
   DCHECK(client_);
   DCHECK(account_tracker_service_);
 }

components/signin/core/browser/signin_manager_base.h

@@ -255,8 +255,6 @@ class SigninManagerBase {
 
   signin::AccountConsistencyMethod account_consistency_;
 
-  base::WeakPtrFactory<SigninManagerBase> weak_pointer_factory_;
-
   DISALLOW_COPY_AND_ASSIGN(SigninManagerBase);
 };