Revert opensearch-project#6681 on 2.x since need more test coverage

Signed-off-by: Huan Jiang <seraphjiang@gmail.com>

CHANGELOG.md

@@ -66,7 +66,6 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - [Multiple Datasource] Able to Hide "Local Cluster" option from datasource DropDown ([#5827](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5827))
 - [Multiple Datasource] Add api registry and allow it to be added into client config in data source plugin ([#5895](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5895))
 - [Multiple Datasource] Refactor client and legacy client to use authentication registry ([#5881](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5881))
-- [Theme] Make theme and dark mode settings user/device specific (in local storage), with opt-out ([#5652](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5652))
 
 ### 🐛 Bug Fixes
 

src/core/public/osd_bootstrap.test.ts

@@ -34,7 +34,6 @@ import { __osdBootstrap__ } from './';
 describe('osd_bootstrap', () => {
   beforeAll(() => {
     const metadata = {
-      branding: { darkMode: 'true' },
       i18n: { translationsUrl: 'http://localhost' },
       vars: { apmConfig: null },
     };

src/core/public/osd_bootstrap.ts

@@ -38,11 +38,6 @@ export async function __osdBootstrap__() {
     document.querySelector('osd-injected-metadata')!.getAttribute('data')!
   );
 
-  const globals: any = typeof window === 'undefined' ? {} : window;
-  const themeTag: string = globals.__osdThemeTag__ || '';
-
-  injectedMetadata.branding.darkMode = themeTag.endsWith('dark');
-
   let i18nError: Error | undefined;
   const apmSystem = new ApmSystem(injectedMetadata.vars.apmConfig, injectedMetadata.basePath);
 

src/core/public/ui_settings/ui_settings_client.ts

@@ -58,13 +58,6 @@ export class UiSettingsClient implements IUiSettingsClient {
     this.defaults = cloneDeep(params.defaults);
     this.cache = defaultsDeep({}, this.defaults, cloneDeep(params.initialSettings));
 
-    if (
-      this.cache['theme:enableUserControl']?.userValue ??
-      this.cache['theme:enableUserControl']?.value
-    ) {
-      this.cache = defaultsDeep(this.cache, this.getBrowserStoredSettings());
-    }
-
     params.done$.subscribe({
       complete: () => {
         this.update$.complete();
@@ -180,28 +173,6 @@ You can use \`IUiSettingsClient.get("${key}", defaultValue)\`, which will just r
     return this.updateErrors$.asObservable();
   }
 
-  private getBrowserStoredSettings() {
-    const uiSettingsJSON = window.localStorage.getItem('uiSettings') || '{}';
-    try {
-      return JSON.parse(uiSettingsJSON);
-    } catch (error) {
-      this.updateErrors$.next(error);
-    }
-    return {};
-  }
-
-  private setBrowserStoredSettings(key: string, newVal: any) {
-    const oldSettings = this.getBrowserStoredSettings();
-    const newSettings = cloneDeep(oldSettings);
-    if (newVal === null) {
-      delete newSettings[key];
-    } else {
-      newSettings[key] = { userValue: newVal };
-    }
-    window.localStorage.setItem(`uiSettings`, JSON.stringify(newSettings));
-    return { settings: newSettings };
-  }
-
   private assertUpdateAllowed(key: string) {
     if (this.isOverridden(key)) {
       throw new Error(
@@ -227,18 +198,8 @@ You can use \`IUiSettingsClient.get("${key}", defaultValue)\`, which will just r
     this.setLocally(key, newVal);
 
     try {
-      if (
-        this.cache['theme:enableUserControl']?.userValue ??
-        this.cache['theme:enableUserControl']?.value
-      ) {
-        const { settings } = this.cache[key]?.preferBrowserSetting
-          ? this.setBrowserStoredSettings(key, newVal)
-          : (await this.api.batchSet(key, newVal)) || {};
-        this.cache = defaultsDeep({}, defaults, this.getBrowserStoredSettings(), settings);
-      } else {
-        const { settings } = (await this.api.batchSet(key, newVal)) || {};
-        this.cache = defaultsDeep({}, defaults, settings);
-      }
+      const { settings } = await this.api.batchSet(key, newVal);
+      this.cache = defaultsDeep({}, defaults, settings);
       this.saved$.next({ key, newValue: newVal, oldValue: initialVal });
       return true;
     } catch (error) {