trivial doc patch -- Twisted Matrix no longer necessary

diff -r 9bf6f907b3ff docs/src/user/installation.tex
@@ -24,11 +24,6 @@
 \item [$\dag$] The Linux hotplug system\footnote{Available from {\tt
       http://linux-hotplug.sourceforge.net/}} (e.g., \path{/sbin/hotplug}
       and related scripts)
-\item [$\dag$] An installation of Twisted~v1.3 or
-  above\footnote{Available from {\tt http://www.twistedmatrix.com}}.
-  There may be a binary package available for your distribution;
-  alternatively it can be installed by running `{\sl make
-    install-twisted}' in the root of the Xen source tree.
 \item [$*$] Build tools (gcc v3.2.x or v3.3.x, binutils, GNU make).
 \item [$*$] Development installation of libcurl (e.g.,\ libcurl-devel).
 \item [$*$] Development installation of zlib (e.g.,\ zlib-dev).

diff -r 9bf6f907b3ff docs/src/user/installation.tex
@@ -24,11 +24,6 @@
 \item [$\dag$] The Linux hotplug system\footnote{Available from {\tt
       http://linux-hotplug.sourceforge.net/}} (e.g., \path{/sbin/hotplug}
       and related scripts)
-\item [$\dag$] An installation of Twisted~v1.3 or
-  above\footnote{Available from {\tt http://www.twistedmatrix.com}}.
-  There may be a binary package available for your distribution;
-  alternatively it can be installed by running `{\sl make
-    install-twisted}' in the root of the Xen source tree.
 \item [$*$] Build tools (gcc v3.2.x or v3.3.x, binutils, GNU make).
 \item [$*$] Development installation of libcurl (e.g.,\ libcurl-devel).
 \item [$*$] Development installation of zlib (e.g.,\ zlib-dev).