Uninstalling EWWW Image Optimizer
Don't! Okay, you're here, so you probably want to know how to uninstall the plugin, but I hope you come back some day! You can also use this to reference where EWWW IO stores information/files. So without further adieu...
- Remove tables: wp_ewwwio_images and wp_ewwwio_queue are where most of the data is stored. You can even empty the tables from Tools->EWWW Image Optimizer with the Erase Optimization History and Clear Queue buttons.
- Remove options: All of the options are prefixed with ewww_image_optimizer_ or exactdn_ (Easy IO options). However, there are some "transients" that use ewwwio_ or ewww_ (and transients themselves are usually prefixed with "wp_"). You should just be able to use any transients cleanup plugin to clear those out if you don't want to just delete everything that matches %ewww%.
- Remove files: EWWW IO stores the debug.log file, the optimization binaries/tools, and any auto-generated lazy load placeholders in the wp-content/ewww/ folder. If you've converted images between formats and left the originals, or converted images to WebP, those are stuck (for now), but we will soon have the ability to clean those up from Tools->EWWW Image Optimizer.
Note that deactivating the plugin from the WP admin will automatically trigger a cleanup of the tools in wp-content/ewww/ so you don't really need to remove those manually.
If you've been using EWWW IO for a very long time, you might also find data stored in the attachment metadata. You can go to Tools->EWWW Image Optimizer->Migrate Optimization Records to move this data to the ewwwio_images table.