users: Remove redundant get_role_for_new_user in lib/create_user.py.

The function get_role_for_new_user was added to get role from the
invited_as value, as invited_as values were one of (1,2,3,4)
previously, but it was then changed to be the actual role value,
i.e. one of (100, 200, 400, 600), in 1f8f227444.

So, we can safely remove this function now and use invited_as value
directly and handle realm_creation case by using an if condition.

zerver/lib/create_user.py

@@ -7,15 +7,7 @@ from django.utils.timezone import now as timezone_now
 from zerver.lib.hotspots import copy_hotspots
 from zerver.lib.upload import copy_avatar
 from zerver.lib.utils import generate_api_key
-from zerver.models import (
-    PreregistrationUser,
-    Realm,
-    Recipient,
-    Stream,
-    Subscription,
-    UserProfile,
-    get_fake_email_domain,
-)
+from zerver.models import Realm, Recipient, Stream, Subscription, UserProfile, get_fake_email_domain
 
 
 def copy_user_settings(source_profile: UserProfile, target_profile: UserProfile) -> None:
@@ -57,16 +49,6 @@ def get_display_email_address(user_profile: UserProfile) -> str:
     return user_profile.delivery_email
 
 
-def get_role_for_new_user(invited_as: int, realm_creation: bool = False) -> int:
-    if realm_creation or invited_as == PreregistrationUser.INVITE_AS["REALM_OWNER"]:
-        return UserProfile.ROLE_REALM_OWNER
-    elif invited_as == PreregistrationUser.INVITE_AS["REALM_ADMIN"]:
-        return UserProfile.ROLE_REALM_ADMINISTRATOR
-    elif invited_as == PreregistrationUser.INVITE_AS["GUEST_USER"]:
-        return UserProfile.ROLE_GUEST
-    return UserProfile.ROLE_MEMBER
-
-
 # create_user_profile is based on Django's User.objects.create_user,
 # except that we don't save to the database so it can used in
 # bulk_creates