Remove STATE_CLASS_TOTAL and last_reset from sensor

[emontnemery]

Proposed change

Simplify sensor:

• Remove STATE_CLASS_TOTAL
• Remove the last_reset attribute from sensor

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR is related to issue:
• Link to documentation pull request: Update documentation and dev blog post with removal of STATE_CLASS_TOTAL and SensorEntity.last_reset developers.home-assistant#1028

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• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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• Documentation added/updated for www.home-assistant.io

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[Danielhiversen]

Regarding Mill:
The values are reset to 0, but the first value we receive might not be 0 (It is not updated that often)
Will it still be correct to use STATE_CLASS_TOTAL_INCREASING ? Is it always assumed that the value is reset to 0?

[frenck]

@Danielhiversen That is solved by #54751

[Danielhiversen]

Ahh, then the changes to the Mill integration looks good 👍

[fsaris]

Okay with #54523 this was added and there was also some reasoning added to the PR about the idea behind it.

Now one of the new state classes is removed. I think this is because total is equal to measurement and obsolete.

But can not follow it fully. Where are such changes discussed and documented? Searched PR messages here, the discussion's on the architecture repo and discord. Try to understand and follow the changes (my way of getting into HA development and see where I can contribute 😄 )

[emontnemery]

@fsaris the blog post introducing #54523 has been updated as well

[balloob]

Suggested change

	"Assistant Core 2021.11. Please update your configuration if "
	"state_class is manually configured, otherwise %s",
	"Assistant Core 2021.11. Please update your configuration and set state class to 'total_increasing' if "
	"state_class is manually configured, otherwise %s",