Consider removing @types/* packages from the build's node_modules folder

[azasypkin]

Currently some packages we depend on declare @types/* as "normal" dependencies (e.g. @slack/client) so they are included into our build packages (license file, package.json and readme file for every such package).

I can't think of any reason why we'd want to have these packages included into build, so should we just add @types/* into CleanExtraFilesFromModulesTask?