Remove the migration code from content_settings::PrefProvider.

components/content_settings/core/common/pref_names.cc

Index: components/content_settings/core/common/pref_names.cc
diff --git a/components/content_settings/core/common/pref_names.cc b/components/content_settings/core/common/pref_names.cc
index 71818e2c1eb3c3ca2e2787af97a4ee6fb3f7e008..7e99756a91e3e1f5c49b4f1299fce7dac8df47d1 100644
--- a/components/content_settings/core/common/pref_names.cc
+++ b/components/content_settings/core/common/pref_names.cc
@@ -13,12 +13,6 @@ const char kBlockThirdPartyCookies[] = "profile.block_third_party_cookies";
 // Version of the pattern format used to define content settings.
 const char kContentSettingsVersion[] = "profile.content_settings.pref_version";
 
-// Patterns for mapping origins to origin related settings. Default settings
-// will be applied to origins that don't match any of the patterns. The pattern
-// format used is defined by kContentSettingsVersion.
-const char kContentSettingsPatternPairs[] =
-    "profile.content_settings.pattern_pairs";
-
 // Integer that specifies the index of the tab the user was on when they
 // last visited the content settings window.
 const char kContentSettingsWindowLastTabIndex[] =
@@ -148,12 +142,6 @@ const char kContentSettingsSiteEngagementPatternPairs[] =
 const char kContentSettingsDurableStoragePatternPairs[] =
     "profile.content_settings.exceptions.durable_storage";
 
-// Whether the patern pairs have been migrated from the deprecated aggregate
-// preference |kContentSettingsPatternPairs| to the separate preferences
-// |kContentSettings<type>PatternPairs|.
-const char kMigratedContentSettingsPatternPairs[] =
-    "profile.migrated_content_settings_exceptions";
-
 // Preferences that are exclusively used to store managed values for default
 // content settings.
 const char kManagedDefaultCookiesSetting[] =