Several Components: Remove obsolete API

[danielchalmers]

Description

@ScarletKuro gave me this list:
MudBooleanInput.cs, DialogService.cs, IFormComponent.cs, ScrollManager.cs, MudAvatar.razor.cs, MudFormComponent.cs, MudDataGrid.razor.cs

This PR takes care of most of them and does some light code cleanup as well since those files will be conflicted anyway.

MudAvatar and MudDataGrid will come after this and #8562 have been merged.

#8472 will help with future removals + cleanups like this

How Has This Been Tested?

Types 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)

Checklist:

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

[danielchalmers]

Let me know of any more obsoletes to remove in the next PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.75%. Comparing base (e6741bb) to head (11b1a29).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8564      +/-   ##
==========================================
+ Coverage   89.52%   89.75%   +0.22%     
==========================================
  Files         411      411              
  Lines       11848    11818      -30     
  Branches     2362     2362              
==========================================
  Hits        10607    10607              
+ Misses        713      683      -30     
  Partials      528      528              

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[henon]

Added to v7.0.0 Migration Guide #8447

[henon]

Thanks!