Remove XamlPreCompile dependency, use CoreCompile

This fixes an the reference list not yet being built.

src/Uno.SourceGeneratorTasks.Dev15.0/Content/Uno.SourceGenerationTasks.targets

@@ -22,7 +22,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-	<UnoSourceGeneratorBeforeTarget Include="XamlPreCompile" />
 	<UnoSourceGeneratorBeforeTarget Include="CoreCompile" />
 
 	<SourceGeneratorInput Include="@(Compile)" />