Remove rails-dev-boost gem from default set of gems for development

Since rails 3.2 there were radical improvements in reloading the code,
not making the rails-dev-boost as useful as before. Using it however
breaks the doc reloading feature in development mode.

If somebody misses that, he can still add it to some
bundler.d/local_*.rb file
Merge pull request #3300 from iNecas/remove-devel-boost

Remove rails-dev-boost gem from default set of gems for development