Remove invalid Signal Strength device class from NETGEAR

[frenck]

Proposed change

The NETGEAR signal strength sensor provides a signal strength in %, which is not a supported unit of measurement for the signal_strength device class.

This PR removes this occurrence as reported in #85361

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)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Entity sensor.daikin_signal_strength (<class 'homeassistant.components.netgear.sensor.NetgearSensorEntity'>) is using native unit of measurement '%' which is not a valid unit for the device class ('signal_strength') it is using #85361
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

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

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• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

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[home-assistant]

Hey there @hacf-fr, @Quentame, @starkillerOG, mind taking a look at this pull request as it has been labeled with an integration (netgear) you are listed as a code owner for? Thanks!

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