PGMap: remove pool max_avail scale factor

PGMap: remove pool max_avail scale factor

The scaling of max_avail by the ratio of non-degraded to total objects
count results in the reported max_avail increasing proportionally to the
number of OSDs marked `down` but not `out`.  This is counter intuitive
since OSDs going `down` should never result in more space being
available.

Removing the scale factor allows max_avail to remain unchanged until the
OSDs are marked `out`.

Signed-off-by: Michael J. Kidd <linuxkidd@gmail.com>
(cherry picked from commit 4de57e904cffbf134b25b28f46caccebfc4456b1)