You certainly 'can' skip the AWA essays when taking the practice tests, but you 'shouldn't' ever do it, and there are a few reasons why.
Apart from the obvious fact that you need to practice writing essays in order to get a high score on the AWA section, the most important reason why you should not skip this section during practice is that it inflates your overall score.
If you skip the essay section during practice, you’ll be forfeiting 60 minutes of the total test time, which means you are going to have to sit for 2 hours and 45 minutes only. This translates into an inflated overall score during practice, because you are just that much more active than you will be on test day.
Read more about the effects of skipping the AWA section here: crunchprep.com/gre-essay-section-importance