api: Expose server_needs_upgrade in register response.

Expose the boolean value server_needs_upgrade in the
responses for register api so that it can be used
by mobile and terminal clients as well.
Highlighted in api changelog as part of
feature level 74 in commit fb93c96
(next commit).

zerver/lib/home.py

@@ -8,7 +8,6 @@ from django.http import HttpRequest
 from django.utils import translation
 from two_factor.utils import default_device
 
-from zerver.lib.compatibility import is_outdated_server
 from zerver.lib.events import do_events_register
 from zerver.lib.i18n import (
     get_and_set_request_language,
@@ -186,7 +185,6 @@ def build_page_params_for_home_page_load(
         test_suite=settings.TEST_SUITE,
         poll_timeout=settings.POLL_TIMEOUT,
         insecure_desktop_app=insecure_desktop_app,
-        server_needs_upgrade=is_outdated_server(user_profile),
         login_page=settings.HOME_NOT_LOGGED_IN,
         save_stacktraces=settings.SAVE_FRONTEND_STACKTRACES,
         warn_no_email=settings.WARN_NO_EMAIL,