We disabled GC due in pg_query to work around
https://github.com/pganalyze/pg_query/issues/226, but this turned out to
be a bug where the Ruby garbage collector might incorrectly garbage
collect an intermediate variable
(https://bugs.ruby-lang.org/issues/18140#note-2).

https://github.com/pganalyze/pg_query/pull/227 works around the problem
by calling to_ary to ensure the Ruby interpreter does not do this. As a
result, we can remove the workaround.