Hide 3PID discovery sections when no identity server

This hides the email and phone sections of Discovery in the Settings when there
is no IS, as they can't meaningfully be used.

Part of element-hq/element-web#10528

src/components/views/settings/tabs/user/GeneralUserSettingsTab.js

@@ -189,13 +189,17 @@ export default class GeneralUserSettingsTab extends React.Component {
         const PhoneNumbers = sdk.getComponent("views.settings.discovery.PhoneNumbers");
         const SetIdServer = sdk.getComponent("views.settings.SetIdServer");
 
+        const threepidSection = this.state.haveIdServer ? <div>
+            <span className="mx_SettingsTab_subheading">{_t("Email addresses")}</span>
+            <EmailAddresses />
+
+            <span className="mx_SettingsTab_subheading">{_t("Phone numbers")}</span>
+            <PhoneNumbers />
+        </div> : null;
+
         return (
             <div className="mx_SettingsTab_section">
-                <span className="mx_SettingsTab_subheading">{_t("Email addresses")}</span>
-                <EmailAddresses />
-
-                <span className="mx_SettingsTab_subheading">{_t("Phone numbers")}</span>
-                <PhoneNumbers />
+                {threepidSection}
                 { /* has its own heading as it includes the current ID server */ }
                 <SetIdServer />
             </div>