Remove obselete phases templates

[mmitche]

These got replaced by the job templates a long time ago and no longer recieve updates. There are only two places in dotnet (cli-migrate and dotnet-cli-archiver) that have references in their main branch, and they are both archived repos.

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation

[riarenas]

FYI @chcosta