Remove NexoScans

[choppeh]

Closes #3118

Checklist:

• [ ] Updated extVersionCode value in build.gradle for individual extensions
• [ ] Updated overrideVersionCode or baseVersionCode as needed for all multisrc extensions
• [ ] Referenced all related issues in the PR body (e.g. "Closes #xyz")
• [ ] Added the isNsfw = true flag in build.gradle when appropriate
• [ ] Have not changed source names
• [ ] Have explicitly kept the id if a source's name or language were changed
• [ ] Have tested the modifications by compiling and running the extension through Android Studio
• [ ] Have removed web_hi_res_512.png when adding a new extension