Revert "add posibility to use 'autopart' or 'part' in redhat's kickstart...

..."

This reverts commit 104b066.  Making it possible for users to customize the
partition layout is highly undesirable with the other committers, to
my surprise.

Given that, this is being reverted.  Users who want this capability are
expected to build their own model to implement it.

This reverts #474.