Delete HNDTYPE_WEAK_NATIVE_COM when no longer needed.

HNDTYPE_WEAK_NATIVE_COM is no longer used in the VM, but some related functionality is still present to ensure that clrgc.dll is compatible with .NET 7.0

Once we do not have the compatibility requirement the remaining pieces of HNDTYPE_WEAK_NATIVE_COM support can be deleted.

See: https://github.com/dotnet/runtime/pull/77196