[netcore] Enable Copy tests that depend on file size differences
[netcore] Enable Copy tests that depend on file size differences

Specifically:

          Microsoft.Build.UnitTests.CopyNotHardLink_Tests.DoCopyOverDifferentFile
          Microsoft.Build.UnitTests.CopySymbolicLink_Tests.DoCopyOverDifferentFile
          Microsoft.Build.UnitTests.CopyHardLink_Tests.DoCopyOverDifferentFile

Possibly fixed by the earlier commit:

commit 2b21ae070fa68de3e5dc5e426f8f9d7a4e9d913e
Author: Ankit Jain <ankit.jain@xamarin.com>
Date:   Thu Jul 20 15:14:05 2017 -0400

    Copy task: Use file sizes tool for skip checks, on !windows

rainersigwald/msbuild,rainersigwald/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,mono/msbuild,chipitsine/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,mono/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,mono/msbuild,mono/msbuild,chipitsine/msbuild,Microsoft/msbuild,chipitsine/msbuild,jeffkl/msbuild,Microsoft/msbuild,jeffkl/msbuild,cdmihai/msbuild,jeffkl/msbuild,Microsoft/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,rainersigwald/msbuild