Delete Users without a First and Last Name

Replace the prefix in wp_users and wp_usermeta table names for the one you use.
Make backup of data from both tables before you start to delete users.

DELETE u FROM wp_users u
  LEFT JOIN wp_usermeta um1 ON u.id = um1.user_id AND um1.meta_key = 'first_name'
  LEFT JOIN wp_usermeta um2 ON u.id = um2.user_id AND um2.meta_key = 'last_name'
WHERE (um1.meta_value IS NULL OR CHAR_LENGTH(um1.meta_value) = 0)
  AND (um2.meta_value IS NULL OR CHAR_LENGTH(um2.meta_value) = 0);

DELETE um FROM wp_usermeta um
  LEFT JOIN wp_users u ON u.id = um.user_id 
WHERE u.id IS NULL;