Remove MudPopoverService

[ScarletKuro]

Description

Remove the old MudPopoverService that was decided to be kept for v7. Now it's time for it to go.

Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.66%. Comparing base (28bc599) to head (36a8065).
Report is 534 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #9957      +/-   ##
==========================================
+ Coverage   89.82%   90.66%   +0.83%     
==========================================
  Files         412      407       -5     
  Lines       11878    12596     +718     
  Branches     2364     2457      +93     
==========================================
+ Hits        10670    11420     +750     
+ Misses        681      613      -68     
- Partials      527      563      +36     

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[ScarletKuro]

Added to v8.0.0 Migration Guide #9953