[ReadingList] Removed dead code and deprecate pref

Introduced in https://codereview.chromium.org/2599293003, it looks like
the last caller of these APIs was removed with
https://chromium-review.googlesource.com/1232959.

Bug: 1386158
Change-Id: If1d548073adde52e0a4310891378b52edb672d25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4078968
Reviewed-by: David Roger <[email protected]>
Reviewed-by: Olivier Robin <[email protected]>
Reviewed-by: Peter Boström <[email protected]>
Reviewed-by: Dominic Battré <[email protected]>
Commit-Queue: Mikel Astiz <[email protected]>
Auto-Submit: Mikel Astiz <[email protected]>
Commit-Queue: David Roger <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1080254}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 5c04d83..c62487f6 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -134,6 +134,7 @@
 #include "components/prefs/pref_service.h"
 #include "components/privacy_sandbox/privacy_sandbox_prefs.h"
 #include "components/proxy_config/pref_proxy_config_tracker_impl.h"
+#include "components/reading_list/core/reading_list_pref_names.h"
 #include "components/safe_browsing/content/common/file_type_policies_prefs.h"
 #include "components/safe_browsing/core/common/safe_browsing_prefs.h"
 #include "components/search_engines/template_url_prepopulate_data.h"
@@ -2089,6 +2090,10 @@
   profile_prefs->ClearPref(kAutofillAssistantTriggerScriptsEnabled);
   profile_prefs->ClearPref(kAutofillAssistantTriggerScriptsIsFirstTimeUser);
 
+  // Added 12/2022.
+  profile_prefs->ClearPref(
+      reading_list::prefs::kDeprecatedReadingListHasUnseenEntries);
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_PROFILE_PREFS