chore: remove unused SourceLink package versions

Deleted the centrally managed Microsoft.SourceLink package versions from
Directory.Packages.props.

Author: matt-edmondson

Directory.Packages.props

@@ -3,8 +3,6 @@
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
   </PropertyGroup>
   <ItemGroup>
-    <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="10.0.300" />
-    <PackageVersion Include="Microsoft.SourceLink.AzureRepos.Git" Version="10.0.300" />
     <PackageVersion Include="System.Text.Json" Version="10.0.9" />
     <PackageVersion Include="ktsu.Semantics.Strings" Version="1.1.3" />
     <PackageVersion Include="Polyfill" Version="10.11.0" />