Load rpy2.ipython for rmagic, print deprecation warning
Remove rmagic tests
Remove rmagic docs

Leaving intersphinx link to rpy2 docs.
No need to check for rpy2 in test machinery
Docs fixes for rmagic deprecation
Add URL to warning about rpy2
Merge pull request #6290 from takluyver/deprecate-rmagic

Deprecate rmagic