Revert "separate database adapter by group in Gemfile"
Revert "separate database adapter by group in Gemfile"

This reverts commit 0047696bc6f4773be2cbaee0c7385fca98b4b4f9.

fukajun/lokka,fjordllc/jobs-fjord-jp,kmamiya/lokka,komagata/docs-komagata-org,jiikko/blog,jiikko/blog,fjordllc/jobs-fjord-jp,morygonzalez/portalshit.net,komagata/docs-komagata-org,willnet/lokka,fjordllc/blog-kowabana-jp,lokka/lokka,horaotoko/kowabana_movie,komagata/docs-komagata-org,machida/zurui-book,hrysd/lokka,ychubachi/yc-lokka,morygonzalez/lokka,horaotoko/horaotoko_F-rik-l,willnet/lokka,morygonzalez/lokka,grooves/annex-forkwell,machida/zurui-book,fukajun/lokka,kmamiya/lokka,cheria/try_lokka,morygonzalez/lokka,komagata/docs-komagata-org,jiikko/blog,fjordllc/blog-kowabana-jp,machida/kuroigamen,lokka/lokka,grooves/annex-forkwell,horaotoko/kowabana_movie,ychubachi/yc-lokka,lokka/lokka,wakate/wakate.org-lokka,hirotaka/blog-hirotaka,willnet/lokka,wakate/wakate.org-lokka,morygonzalez/portalshit.net,jiikko/blog,morygonzalez/portalshit.net,ychubachi/yc-lokka,horaotoko/horaotoko_F-rik-l,fukajun/lokka,lokka/lokka,grooves/annex-forkwell,hirotaka/blog-hirotaka,cheria/try_lokka,machida/kuroigamen,kmamiya/lokka,morygonzalez/portalshit.net,hirotaka/blog-hirotaka,hrysd/lokka