fix zpool list property names

This change is based on
r354380 8899 zpool list property documentation doesn't match actual behaviour

There is no "used" pool property, "alloc" is actually spelled
"allocated".

MFC after:	5 days

cddl/contrib/opensolaris/cmd/zpool/zpool.8

@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 20, 2019
+.Dd November 7, 2019
 .Dt ZPOOL 8
 .Os
 .Sh NAME
@@ -602,8 +602,8 @@ Each pool has several properties associated with it. Some properties are
 read-only statistics while others are configurable and change the behavior of
 the pool. The following are read-only properties:
 .Bl -tag -width "dedupratio"
-.It Sy alloc
-Amount of storage space within the pool that has been physically allocated.
+.It Sy allocated
+Amount of storage space used within the pool.
 .It Sy capacity
 Percentage of pool space used. This property can also be referred to by its
 shortened column name, "cap".
@@ -653,8 +653,6 @@ Information about unsupported features that are enabled on the pool.
 See
 .Xr zpool-features 7
 for details.
-.It Sy used
-Amount of storage space used within the pool.
 .El
 .Pp
 The space usage properties report actual physical space available to the
@@ -1576,8 +1574,8 @@ Comma-separated list of properties to display. See the
 section for a list of valid properties. The default list is
 .Sy name ,
 .Sy size ,
-.Sy used ,
-.Sy available ,
+.Sy allocated ,
+.Sy free ,
 .Sy checkpoint ,
 .Sy expandsize ,
 .Sy fragmentation ,