Disable doc processing, as we're likely to bump into xslt bugs.

Signed-off-by: Lucas C. Villa Real <lucasvr@gobolinux.org>

--- apt-2.1.11/doc/CMakeLists.txt.orig	2020-11-18 17:40:05.316126229 -0300
+++ apt-2.1.11/doc/CMakeLists.txt	2020-11-18 17:40:45.406125733 -0300
@@ -67,33 +67,3 @@ install(DIRECTORY  ${PROJECT_BINARY_DIR}
 )
 
 endif()
-
-add_docbook(apt-man MANPAGE ALL
-    DOCUMENTS
-        apt.8.xml
-        apt_auth.conf.5.xml
-        apt-cache.8.xml
-        apt-cdrom.8.xml
-        apt.conf.5.xml
-        apt-config.8.xml
-        apt-extracttemplates.1.xml
-        apt-ftparchive.1.xml
-        apt-get.8.xml
-        apt-key.8.xml
-        apt-mark.8.xml
-        apt_preferences.5.xml
-        apt-patterns.7.xml
-        apt-secure.8.xml
-        apt-sortpkgs.1.xml
-        apt-transport-http.1.xml
-        apt-transport-https.1.xml
-        apt-transport-mirror.1.xml
-        sources.list.5.xml
-    DEPENDS ${ENTITIES}
-    TRANSLATED_ENTITIES ${TRANSLATED_ENTITIES}
-    LINGUAS ${LINGUAS}
-)
-
-add_update_po4a(update-po4a po/${PROJECT_NAME}-doc.pot "po/header.pot.txt")
-
-add_subdirectory(examples)