Remove unnecessary `tryCatch()` statements targeting `insight::download_model()`

[IndrajeetPatil]

There are many such instances in this test file:

https://github.com/easystats/performance/blob/c8977486a8f61e8de76840eb29bafb16c0925a6b/tests/testthat/test-model_performance.bayesian.R#L7

insight::download_model() will anyway return NULL in case of an error.