speed up package_list action by only retrieving column we need (not whole package) from db

importing package_revision_table here might be frowned on.  What sorts of optimizations would you consider acceptable?

It would be even faster if we did some `select array(...)` magic in our query, but that might be taking it a little too far.

edit: performance numbers from comments below:

option | time(s) | improvement
--- | ---: | ---:
original | 0.479 | 1.0x
this PR | 0.048 | 10.0x
select array | 0.027 | 17.7x