DB packages cleanup: ruby-dbi, ruby-mysql

[Dmitry Borodaenko <angdraug@gmail.com>]

AFAICT nobody is using Ruby DBI anymore. I originally packaged it as a
dependency of Samizdat and Graffiti, which have been converted to Sequel
since Dec 2011. No other packages in Debian depend on ruby-dbi or
ruby-dbd-*, lets remove them.

Same story with ruby-mysql. It has been superceded by ruby-mysql2, and
only 2 packages in Debian still depend on it: ruby-graffiti and
ruby-opennebula. Both use it via Sequel, which also supports
ruby-mysql2, meaning that both packages are likely to only need a
dependency fix in debian/control.

Thoughts, objections?

-- 
Dmitry Borodaenko