cam/ata: Postpone removal of two compat sysctls until 15
Prefer UNMAPPEDIO and ROTATING from flags sysctl. See
- aeab0812e68c (Add flags sysctl to ada)
- cf3ff63e55e4 (Convert unmappedio over to a flag)
- 96eb32bf0f5a (Convert rotating to a flag bit)
Reviewed by: imp, ken, cam
MFC after: immediately (we want this in 14.0)
Differential Revision: https://reviews.freebsd.org/D42402