[master] Update dependencies from dotnet/core-setup (dotnet/corefx#35713)

[master] Update dependencies from dotnet/core-setup (dotnet/corefx#35713)

* Update dependencies from https://github.com/dotnet/core-setup build 20190301.13

This change updates the following dependencies
- Microsoft.NETCore.App - 3.0.0-preview4-27501-13
- Microsoft.NETCore.DotNetHost - 3.0.0-preview4-27501-13
- Microsoft.NETCore.DotNetHostPolicy - 3.0.0-preview4-27501-13

* Remove workaround for System.Runtime.CompilerServices.Unsafe

* Update dependencies from https://github.com/dotnet/core-setup build 20190302.8

This change updates the following dependencies
- Microsoft.NETCore.App - 3.0.0-preview4-27502-8
- Microsoft.NETCore.DotNetHost - 3.0.0-preview4-27502-8
- Microsoft.NETCore.DotNetHostPolicy - 3.0.0-preview4-27502-8

* Update dependencies from https://github.com/dotnet/core-setup build 20190303.9

This change updates the following dependencies
- Microsoft.NETCore.App - 3.0.0-preview4-27503-9
- Microsoft.NETCore.DotNetHost - 3.0.0-preview4-27503-9
- Microsoft.NETCore.DotNetHostPolicy - 3.0.0-preview4-27503-9

* Update dependencies from https://github.com/dotnet/core-setup build 20190304.10

This change updates the following dependencies
- Microsoft.NETCore.App - 3.0.0-preview4-27504-10
- Microsoft.NETCore.DotNetHost - 3.0.0-preview4-27504-10
- Microsoft.NETCore.DotNetHostPolicy - 3.0.0-preview4-27504-10

* Don't include EventRegistrationToken on Unix

This type was accidentally duplicated between CoreLib and contracts.

Suppress that for now since we're detecting the duplication in the shared framework.

Make a fix in the shared items to restore the condition on this type.

Commit migrated from https://github.com/dotnet/corefx/commit/ae1426803f77356a7bed0b14c505c8b6030b3a6e