PM: Duplicate functionality removed & rename

1) GetPackagesInstaledInSolution() removed. Duplicate, does nothing,
redirects to public available Solution.GetPackages()

2) IsPackageInstaledInSolution() removed. Duplicate, does nothing,
redirects to public available Solution.IsPackageInstalled()

3) Name GetInstalledPackages() renamed to GetPackages().
Misleading name, all packages are installed in
selected-projects/project/solution.
Or packages exist in repository, where repository can be
available/solution/project/installed.