mypy: Use upstream types for asgiref, natsort.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

pyproject.toml

@@ -49,7 +49,6 @@ no_implicit_reexport = false
 module = [
     "ahocorasick.*",
     "aioapns.*",
-    "asgiref.*",
     "bitfield.*",
     "bmemcached.*",
     "bson.*",
@@ -76,7 +75,6 @@ module = [
     "ldap.*",
     "markdown_include.*",
     "moto.*",
-    "natsort.*",
     "onelogin.*",
     "openapi_core.*",
     "premailer.*",