Removed Makefile.in targets that refer to the `doc/design' directory.

Patch by: Bhuvaneswaran <bhuvan@ubuntu.com>
Suggested by: madanus
Reviewed by: madanus

* Makefile.in
  (doc-design, doc-design-html, doc-design-pdf, doc-design-ps): Deleted.
  (doc): Removed dependency on doc-design.
  (doc-all-html): Removed dependency on doc-design-html.
  (doc-all-pdf): Removed dependency on doc-design-pdf.
  (doc-all-ps): Removed dependency on doc-design-ps.