navReducer [nfc]: Remove an initial: true params hack.

In the previous commit, we removed our last call site of
`getStateWithRoute` where 'realm' was passed for `route`. Therefore,
this conditional can disappear.

See more about this hack at
zulip#4273 (comment).

Author: chrisbobbe

src/nav/navReducer.js

@@ -11,17 +11,7 @@ import { INITIAL_FETCH_COMPLETE, ACCOUNT_SWITCH, LOGIN_SUCCESS, LOGOUT } from '.
  * Private; exported only for tests.
  */
 export const getStateForRoute = (route: string): NavigationState => {
-  // TODO: this is kind of a hack!  Refactor to a better way.
-  //  * Perhaps pass `initial: true` unconditionally in this initialization
-  //    code, to all routes?  Then that'd just be part of the interface of
-  //    making a screen work as an initial screen.
-  //  * Alternatively, we could replace the whole system of `ModalNavBar`,
-  //    `canGoBack`, etc., with our own "navigation view" that would be more
-  //    directly integrated into the navigation framework:
-  //      https://reactnavigation.org/docs/en/2.x/navigation-views.html
-  const params = route === 'realm' ? { initial: true } : undefined;
-
-  const action = AppNavigator.router.getActionForPathAndParams(route, params);
+  const action = AppNavigator.router.getActionForPathAndParams(route);
   if (!action) {
     // The argument should be a constant string that is a genuine nav route;
     // so this condition can only happen if we've gotten that wrong.

src/start/RealmScreen.js

@@ -24,9 +24,6 @@ type Props = $ReadOnly<{|
     ...NavigationStateRoute,
     params?: {|
       realm: URL | void,
-      // Currently passed as `true` in a hack in `navReducer.js`; see
-      //   https://github.com/zulip/zulip-mobile/pull/4273#discussion_r499114689.
-      // TODO: Stop using that hack.
       initial?: boolean,
     |},
   |}>,