Remove unnecessary suppressions

[mthalman]

When attempting to build the runtime repo with the latest build of .NET 8 Preview 7 SDK, it produces the following errors:

/vmr/src/runtime/artifacts/source-build/self/package-cache/microsoft.dotnet.apicompat.task/8.0.100-preview.7.23364.43/build/Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : Unnecessary suppressions found. The APICompat suppression file can be updated by rebuilding with '/p:ApiCompatGenerateSuppressionFile=true' [/vmr/src/runtime/artifacts/source-build/self/src/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj]
/vmr/src/runtime/artifacts/source-build/self/package-cache/microsoft.dotnet.apicompat.task/8.0.100-preview.7.23364.43/build/Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : CP0001 (Target: 'T:System.Diagnostics.DebuggerGuidedStepThroughAttribute') [/vmr/src/runtime/artifacts/source-build/self/src/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj]
/vmr/src/runtime/artifacts/source-build/self/package-cache/microsoft.dotnet.apicompat.task/8.0.100-preview.7.23364.43/build/Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : CP0001 (Target: 'T:System.Runtime.CompilerServices.EagerStaticClassConstructionAttribute') [/vmr/src/runtime/artifacts/source-build/self/src/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj]
/vmr/src/runtime/artifacts/source-build/self/package-cache/microsoft.dotnet.apicompat.task/8.0.100-preview.7.23364.43/build/Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : CP0016 (Target: 'M:System.Runtime.InteropServices.Marshal.GetObjectForNativeVariant``1(System.IntPtr)->T?:[T:System.Diagnostics.CodeAnalysis.MaybeNullAttribute]') [/vmr/src/runtime/artifacts/source-build/self/src/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj]

This is fixed by removing the unnecessary suppressions from System.Private.CoreLib's CompatibilitySuppressions.xml file.

[mthalman]

Interesting. These seem to be needed for Windows builds but not Linux. This was originally caught from the VMR source-build, which is Linux only. I'll log this as an issue instead since this isn't as straightforward as I thought.

I've logged #89206 instead.