[BioPython] Removing Bio.ECell, Bio.Rebase, Bio.CDD and Bio.SGMLExtractor

[Peter]

Dear all,

The following unmaintained modules were deprecated a couple of
releases ago, and unless anyone objects, they will shortly be removed,
and will not be present in the next release of Biopython:

Bio.ECell - obsolete with ECell updates
Bio.Rebase - could not parse current Rebase records
Bio.CDD - could not parse current HTML files from CDD
Bio.SGMLExtractor - old parsing code no longer needed within Biopython

As usual, the files will still be preserved in CVS so if at a later
date someone wants to resurrect this functionality, this is possible.

Peter