First, there's one mistake made in this situation:
The Package folder is not in the Asset folder, but in the project's root.
This was a small change done to Unity since the 2018 version to allow the engine editor to be more versatile and autonomous when it comes to third party plugins and packages imported into a project. Prior to 2018, most of the things you find in the Packages were either automatically included by default (even if not used) in every Unity builds, or had to be imported in the Editor folder that was outside of the Asset folder.
In the Packages folder, the engine automatically add some "default" packages such as Unity UI, Analytics Library, Unity Ads, etc. The importance of each folder is based on what you need in your project.
Should you erase all of them? While it's possible to erase 99% of them, I suggest you first take a look at each Packages' names. For example, if you use the Unity Colalborate feature (multiple developers working from different station), you need to keep the "Unity Colalborate" package. If you're not using the Legacy UI, but an actual in-scene canvas for the UI/Interaction/buttons, you got to keep the "Unity UI" package. If you plan on having some Advertisement in your game (like on Mobile) and want a relatively quick & easy setup for fetching the ads, the "com.unity.ads" includes some really versatile tools. If you plan on having in-App purchase, there's a default package for that too.
One of the reason why this change was done to the Engine is also to allow a better flow with Unity's Asset Store. Prior to this change, when you bought a plugin in the Asset Store that was supposed to be located in the Editor folder (so that the in-editor tools could be displayed), you had to manually move files around which was a real Q&A issue as someone making a mistake could ended up breaking a project. With the addition of the "Packages" folder, not only is it possible for the Asset Store to add all the Editor & Assets of a plugin into the project folder, but it's also possible to update all those files without any user interaction (other than starting the update from the Asset Store).
If you want to remove those folders, at least I suggest you first do it through the Package Manager (Window/Package Manager). This menu explains what each package does and has a cool little "Remove" button that ensure each package are properly removed. (In the Packages Manager, the installed packages have a checkmark on the right of their version number. Those without a checkmark are available, but not installed in the current project).
