Remove xtag

It is behaving a little bit different from the libxml parser which has
caused weird bugs in the past. Anyway, everybody has libxml (I am
planning to write an Expat parser too but not there yet).

modules/LIST

@@ -359,7 +359,6 @@ $Id$
  * xml: LibXML xml parser
  * xosd: X On Screen Display interface
  * xscreensaver: Xscreensaver inhibition
- * xtag: XTAG xml parser
  * yuv: yuv video output
  * yuvp: YUVP to YUVA/RGBA chroma converter
  * yuy2_i420: yuy2 to 4:2:0 conversions functions

modules/misc/xml/Modules.am

-SOURCES_xtag = xtag.c
 SOURCES_xml = libxml.c
-
-libvlc_LTLIBRARIES += libxtag_plugin.la

po/POTFILES.in

@@ -975,7 +975,6 @@ modules/misc/svg.c
 modules/misc/text_renderer.h
 modules/misc/win32text.c
 modules/misc/xml/libxml.c
-modules/misc/xml/xtag.c
 modules/mmx/memcpy.c
 modules/mmxext/memcpy.c
 modules/mux/asf.c