build: remove legacy Custom Tool wiring for .sdsl/.sdfx

Reintroduced when Stride.Build.Sdk was merged from master (PR stride3d#3085);
sdsl-rewrite had already switched to the Roslyn source generator.
The stale wiring caused VS to regenerate .sdsl.cs/.sdfx.cs on disk,
which then collided with the Roslyn-emitted obj/ files (CS0111/CS0579
duplicate types).

Author: xen2

sources/sdk/Stride.Build.Sdk/Sdk/Sdk.targets

@@ -92,10 +92,6 @@
     <StrideShaderFiles Include="**\*.sdfx" Exclude="$(DefaultItemExcludes);$(DefaultExcludesInProjectFolder)" />
     <AdditionalFiles Include="@(StrideShaderFiles)" />
     <ProjectReference Condition="'@(StrideShaderFiles)' != ''" Include="$(StrideRoot)sources\shaders\Stride.Shaders.Generators\Stride.Shaders.Generators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
-    <Compile Update="**\*.sdsl.cs" DependentUpon="%(Filename)" />
-    <None Update="**\*.sdsl" Generator="StrideShaderKeyGenerator" />
-    <Compile Update="**\*.sdfx.cs" DependentUpon="%(Filename)" />
-    <None Update="**\*.sdfx" Generator="StrideEffectCodeGenerator" />
   </ItemGroup>
 
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