Removed Deprecated for 7.0 (#3435)

Removed:
* Major components:
  * TabView/TabViewItem
  * HeaderedTextBlock
  * FacebookService and Microsoft.Toolkit.Uwp.Services project
  * RSS Parsers
* Smaller methods:
  * StringExtensions.ToSafeString
  * LinkedIn, Twitter and Weibo sync Logout methods.
  * ConnectedAnimations.SetListDataItemForNextConnectedAnnimation
  * TileControl.IsCompositionSupported
  * NotifyTaskCompletion
  * Singleton

This is still missing the update on the docs repo.

## Contributes towards #3062
## Fixes #3396

## PR Type
What kind of change does this PR introduce?
<!-- Please uncomment one or more that apply to this PR. -->

<!-- - Bugfix -->
<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
- Other... Please describe: Removing dead code.


## What is the current behavior?
Obsolete classes marked as obsolete, but still exist in code.

## What is the new behavior?
Some classes/methods marked as obsolete are now removed from code.

## PR Checklist

Please check if your PR fulfills the following requirements:

- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [X] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [ ] Contains **NO** breaking changes

This PR IS a breaking change, as instead of just providing a warning, any developers that uses the dead code will now get missing method/class exceptions.

Author: msftbot[bot]

Microsoft.Toolkit.Parsers/Microsoft.Toolkit.Parsers.csproj

@@ -8,10 +8,8 @@
 
       Markdown: Allows you to parse a Markdown String into a Markdown Document, and then Render it with a Markdown Renderer.
 
-      RSS: Allows you to parse an RSS content String into an RSS Schema.
-
     </Description>
-    <PackageTags>UWP Toolkit Windows Parsers Parsing Markdown RSS</PackageTags>
+    <PackageTags>UWP Toolkit Windows Parsers Parsing Markdown</PackageTags>
   </PropertyGroup>
 
   <ItemGroup>