Update pg_query to v2.1.1

What does this MR do and why?

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.

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