Merge pull request dotnet/corefx#26926 from MarcoRossignoli/issues/26856_GetHostByName

Remove old GetHostByName logic

Commit migrated from https://github.com/dotnet/corefx/commit/643bccc7f2c24a897cc15c42486d4184e1f931eb

diff --cc src/libraries/Native/Unix/configure.cmake
Simple merge

diff --cc src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj
Simple merge

diff --cc src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionPal.Unix.cs
Simple merge