Revert "Try catching the ActiveRecord::RecordNotUnique to detect duplicate tags."

This reverts commit 7be5492f2d43948f9882ae1a238c41e59e12c22c.

This code assumes there is a unique index on tags.name.  Reverting because
adding a unique index on name is custom behavior and not every consumer of
the library will add the index.
Do not make a connection when checking if MySQL is the database