removed bulk_insert test

I tried to install Test::Fixture::DBI with cpanm, but test failed so that I did not able to install it.
I read cpanm's build log and realized that the test examines SQLite failed.
According to the log, the test tries to make sure that SQLite cannot use bulk insert.
However, SQLite is now compatible with bulk insert.
Here is SQLite's release log in 2012 http://www.sqlite.org/releaselog/3_7_11.html
Therefore, if a user have SQLite higher than 3.7.11, its test fails.
I think the subtest 'fail bulk_insert' test is now useless, so it should be removed.