Improve config flow type hints in sms

[epenet]

Proposed change

SSIA, linked to #124316

Also removed unused async_step_import, which appears to have been missed in #43484

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• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• Breaking change (fix/feature causing existing functionality to break)
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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @ocalvo, mind taking a look at this pull request as it has been labeled with an integration (sms) you are listed as a code owner for? Thanks!

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Code owners of sms can trigger bot actions by commenting:

• @home-assistant close Closes the pull request.
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[epenet]

Sadly there is very little coverage on sms integration:

---------- coverage: platform linux, python 3.12.5-final-0 -----------
Name                                          Stmts   Miss  Cover   Missing
---------------------------------------------------------------------------
homeassistant/components/sms/__init__.py         45     27    40%   48-50, 56-94, 99-104
homeassistant/components/sms/config_flow.py      51     51     0%   3-90
homeassistant/components/sms/const.py            12      0   100%
homeassistant/components/sms/coordinator.py      27     14    48%   21-27, 31-35, 43-49, 53-57
homeassistant/components/sms/gateway.py         130     72    45%   31-34, 42-46, 54-82, 115-116, 125-131, 139-145, 149, 153, 157, 161-167, 171, 175-181, 185-191, 195, 200-211
homeassistant/components/sms/notify.py           44     44     0%   3-85
homeassistant/components/sms/sensor.py           29     29     0%   3-120
---------------------------------------------------------------------------
TOTAL                                           338    237    30%

[epenet]

Removed, as it appears to have been missed in #43484

[jbouwh]

Let's open a follow up PR to, at least, add coverage for the config_flow.

LGTM,
Thanks @epenet 👍