chore: Do not include Parquet extension

[krlmlr]

.

[Tmonster]

https://github.com/duckdb/duckdb-r/pull/4#pullrequestreview-1616987668

Realizing this won't working right now as auto-loading will only be in the 0.9.0 release ( so potentially in 2 weeks). I can probably just write the tests to call Install {{extension}}; Load {{extension}} then in 2 weeks update the PR.

[Tmonster]

ok, so GitHub tests to make sure auto-loading extensions is kinda redundant. because the r client and the source can change, it's not guaranteed that the R package can build with a combination of the "bleeding edge" of duckdb-r and the latest release of duckdb.

What you would have to do is checkout the latest commit tags of both duckdb-r and duckdb, and then run a test for extensions. Because both repos will be releases, the R build should succeed, and the auto-loading should work. @hannes is there a release test script/process where I can testing of extension auto-loading in R?