Revert "PLT-1800 Load server side locale from the config.json (#3076)"

This reverts commit 34beaa569b.

webapp/components/user_settings/user_settings_display.jsx

@@ -632,11 +632,7 @@ export default class UserSettingsDisplay extends React.Component {
             );
         }
 
-        const userLocale = this.props.user.locale;
         if (this.props.activeSection === 'languages') {
-            if (!I18n.isLanguageAvailable(userLocale)) {
-                this.props.user.locale = global.window.mm_config.DefaultClientLocale;
-            }
             languagesSection = (
                 <ManageLanguages
                     user={this.props.user}
@@ -647,12 +643,7 @@ export default class UserSettingsDisplay extends React.Component {
                 />
             );
         } else {
-            let locale;
-            if (I18n.isLanguageAvailable(userLocale)) {
-                locale = I18n.getLanguageInfo(userLocale).name;
-            } else {
-                locale = I18n.getLanguageInfo(global.window.mm_config.DefaultClientLocale).name;
-            }
+            var locale = I18n.getLanguageInfo(this.props.user.locale).name;
 
             languagesSection = (
                 <SettingItemMin