Remove obsolete "session expires on IP change" config

- Session always expire on IP change; the config only controlled whether an error message was shown or not

src/main/java/fr/xephi/authme/settings/SettingsMigrationService.java

@@ -82,7 +82,8 @@ public class SettingsMigrationService extends PlainMigrationService {
             "VeryGames", "settings.restrictions.allowAllCommandsIfRegistrationIsOptional", "DataSource.mySQLWebsite",
             "Hooks.customAttributes", "Security.stop.kickPlayersBeforeStopping",
             "settings.restrictions.keepCollisionsDisabled", "settings.forceCommands", "settings.forceCommandsAsConsole",
-            "settings.forceRegisterCommands", "settings.forceRegisterCommandsAsConsole"};
+            "settings.forceRegisterCommands", "settings.forceRegisterCommandsAsConsole",
+            "settings.sessions.sessionExpireOnIpChange"};
         for (String deprecatedPath : deprecatedProperties) {
             if (resource.contains(deprecatedPath)) {
                 return true;

src/main/java/fr/xephi/authme/settings/properties/PluginSettings.java

@@ -22,20 +22,11 @@ public class PluginSettings implements SettingsHolder {
 
     @Comment({
         "After how many minutes should a session expire?",
-        "Remember that sessions will end only after the timeout, and",
-        "if the player's IP has changed but the timeout hasn't expired,",
-        "the player will be kicked from the server due to invalid session"
+        "A player's session ends after the timeout or if his IP has changed"
     })
     public static final Property<Integer> SESSIONS_TIMEOUT =
         newProperty("settings.sessions.timeout", 10);
 
-    @Comment({
-        "Should the session expire if the player tries to log in with",
-        "another IP address?"
-    })
-    public static final Property<Boolean> SESSIONS_EXPIRE_ON_IP_CHANGE =
-        newProperty("settings.sessions.sessionExpireOnIpChange", true);
-
     @Comment({
         "Message language, available languages:",
         "https://github.com/AuthMe/AuthMeReloaded/blob/master/docs/translations.md"