doc: Fix distchek for generated eps file

* doc/Makefile.am (EXTRA_DIST, BUILT_SOURCES): Add
gnupg-module-overview.eps, gnupg-card-architecture.eps
(DISTCLEANFILES): Remove them.

The files needs to be added so that it is properly
included in the dist tarball. As the rule
for it was moved into maintainer mode by 58bab1a.