What do you mean about "trying to remove crawled properties"? Do you want to remove the mapping of a crawled property or delete the unused crawled properties?
If you want to delete the unused crawled properties, you can go to Central Administration > Manage service applications > Search Service Application > Search Schema > Categories, then edit the category which including the crawled property you want to delete. In the edit page, check the option "Delete all unmapped crawled properties" and click OK.
After removing all mappings from the property you also have to remove it from the search index. Click "Edit/Map Property" in the context menu of a crawled property.
- You have removed all mappings for this property.
- Do not include values for this property in the search index
Note: Some OOB SharePoint crawled properties cannot be deleted.
you can also refer to below article for more information about "HOW TO DELETE A CRAWLED PROPERTY". The article is for SP 2010, but it still has good information for you: