Deleted obsolete files pertaining to svn:

acl2-startup-info.txt
bin/svn-info-books
bin/svnc
bin/svncf
bin/svnu

Updated :doc note-7-0:

  Development snapshots of ACL2 (and of the [community-books]) are now
  available between releases from {an ACL2 github repository |
  https://github.com/acl2/acl2}. Thanks to David Rager and Jared
  Davis for taking the lead on this conversion. As a result, the
  banner printed at startup for those snapshots has changed slightly.