Revert "vm_pageout_scans: correct detection of active object"

This reverts commit 3de96d664aaaf8e3fb1ca4fc4bd864d2cf734b24.

Problem is that it is possible to reach the state with ref_count ==
1 for the mapped non-anonymous object. For instance, anonymous posix
shmfd or linux shmfs object could be mapped, and then corresponding
file descriptor closed, dropping the object reference owned by the
shmfd/shmfs file. Then the check in inactive scan assumes that the
object and page are not mapped and frees the page, while they are not.

PR: 261707
Discussed with: markj
Sponsored by: The FreeBSD Foundation
MFC after: now