poolmanager, pool: Drop classic partition and most space cost related code

This patch drops the classic partition. Wass has been the default partition
type for new partitions for a while already. During that time we have not
heard about any issues with wass. Therefore this patch drops the classic
partition type.

Technically, ClassicPartition is kept as a base class for WassPartition, but
the dead code is dropped. A lot of related code for computing the space
cost is dropped as well as it is no longer used.

A number of user visible changes should be documented in the release notes:

- Sites still using the classic partition type must manually update
  poolmanager.conf to create wass partitions instead.

- When switching from classic to wass, it is important to reset cpucostfactor
  and spacecostfactor, as the interpretation of these parameters has changed.
  We suggest to use the default value of 1.0 for both parameters.

- The alternate PoolSelectionUnitV2wgap has been dropped. It can no longer
  be used as a value for the selectionUnit configuration property. We believe
  that this functionality is no longer required when using wass. Should a
  need for such functionality arise in the future, it would better be
  implemented as a new partition type rather than a selection unit.

- The pool manager 'xcm ls' command no longer accepts any arguments or
  options.

- The pool manager 'cm ls' command no longer accepts the -size and -d
  options.

- The pool manager 'getpoolsbylink' command no longer accepts the -size
  option.

- The pool migration module no longer recognizes the source.spaceCost and
  target.spaceCost variables.

- The pool migration module no longer accepts 'best' as a value for
  the -select option.

- The pool manager 'rebalance pgroup' command no longer accepts 'sc' as a
  value for the -metric option. The new value 'free' has been added instead.

- The pool manager 'costCalculation' configuration parameter is obsolete.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Albert Rossi <arossi@fnal.gov>
Patch: http://rb.dcache.org/r/5682/