pybind/mgr: use annotation style without comment

pybind/mgr: use annotation style without comment

* use annotation style without comment
* add noqa to import statement to prevent flake8 from complaining
  those which import typing modules

to silence the warnings like:

```
flake8 run-test: commands[0] | flake8 --config=tox.ini alerts balancer cephadm cli_api crash devicehealth diskprediction_local hello iostat localpool nfs orchestrator prometheus selftest
cephadm/schedule.py:5:1: F401 'typing.Callable' imported but unused
cephadm/schedule.py:8:1: F401 'ceph.deployment.service_spec.ServiceSpec' imported but unused
cephadm/tests/fixtures.py:17:1: F401 'orchestrator.OrchResult' imported but unused
orchestrator/module.py:4:1: F401 'typing.Set' imported but unused
orchestrator/module.py:17:1: F401 'ceph.deployment.inventory.Device' imported but unused
prometheus/module.py:17:1: F401 'typing.DefaultDict' imported but unused
6     F401 'typing.Callable' imported but unused
ERROR: InvocationError for command /home/jenkins-build/build/workspace/ceph-pull-requests/src/pybind/mgr/.tox/flake8/bin/flake8 --config=tox.ini alerts
```

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
(cherry picked from commit 7894e7bdd1c25d86a71e3dcdc88c46062cb31101)

Conflicts:
	src/pybind/mgr/orchestrator/module.py [ commit 28314cebef32
	  ("mgr/cephadm: Adding support for natural sorting") not in
	  pacific ]
	src/pybind/mgr/cephadm/services/exporter.py [ additional
	  pacific-only change, this file doesn't exist in main ]