I have worked with the PackageManagement team over the last months to migrate from a compilation against netcoreapp2.0 (which is not supported any more but still working) and netstandard1.6 to compile against netstandard2.0 instead. PRs that were a pre-requesite for this transition are already approved and merged, the final PR to switch over to netstandard2.0 has now been merged here.
Once PackageManagement releases this change in an upcoming release to the PowerShell Gallery, it will be a breaking change for the WiX installer, which has the DLLs and paths hard-coded here and therefore will need to be updated.
I suggest to remove the netcoreapp2.0 folder in the coreclr folder and rename the netstandard1.6 folder to netstandard2.0 (the number of DLLs and their names remains the same)
Also: is it possible to remove the fullclr folder or would this cause a problem due to a hash mismatch?