README: do not list outdated Microsoft systems

BIND is no longer being built for Windows XP or Windows Server 2003 as
these systems reached end of life, so do not mention them in README.

README

@@ -301,7 +301,7 @@ on many versions of Linux and UNIX, including RedHat, Fedora, Debian,
 Ubuntu, SuSE, Slackware, FreeBSD, NetBSD, OpenBSD, Mac OS X, Solaris,
 HP-UX, AIX, SCO OpenServer, and OpenWRT.
 
-BIND is also available for Windows XP, 2003, 2008, and higher. See
+BIND is also available for Windows Server 2008 and higher. See
 win32utils/readme1st.txt for details on building for Windows systems.
 
 To build on a UNIX or Linux system, use:

README.md

@@ -317,7 +317,7 @@ many versions of Linux and UNIX, including RedHat, Fedora, Debian, Ubuntu,
 SuSE, Slackware, FreeBSD, NetBSD, OpenBSD, Mac OS X, Solaris, HP-UX, AIX,
 SCO OpenServer, and OpenWRT. 
 
-BIND is also available for Windows XP, 2003, 2008, and higher.  See
+BIND is also available for Windows Server 2008 and higher.  See
 `win32utils/readme1st.txt` for details on building for Windows systems.
 
 To build on a UNIX or Linux system, use: