Bookmark Suggestions: don't use creation date fallback by default

The code stays around for now, so we can turn it on via a variation param if required.

BUG=640566

Review-Url: https://codereview.chromium.org/2279273002
Cr-Commit-Position: refs/heads/master@{#414703}

components/ntp_snippets/bookmarks/bookmark_suggestions_provider.cc

@@ -34,7 +34,7 @@ namespace {
 const int kMaxBookmarks = 10;
 const int kMinBookmarks = 3;
 const int kMaxBookmarkAgeInDays = 42;
-const int kUseCreationDateFallbackForDays = 42;
+const int kUseCreationDateFallbackForDays = 0;
 
 const char* kMaxBookmarksParamName = "bookmarks_max_count";
 const char* kMinBookmarksParamName = "bookmarks_min_count";