independent layer of the virtual memory system.  Update some of the nearby
comments to eliminate redundancy and improve clarity.

In vm/vm_reserv.c, do not use hyphens after adverbs ending in -ly per
The Chicago Manual of Style.

Update the comment in vm/vm_page.h defining the four types of page queues to
reflect the elimination of PG_CACHED pages and the introduction of the
laundry queue.

Reviewed by:	kib, markj
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D8752