xend: fix a regression in c/s 19791.

Using changeset 19791:c0d2838fc10f, I can't create an HVM.
xend.log shows:

  File "usr/lib64/python2.4/site-packages/xen/xend/image.py", line
  759, in configure
    store_dmargs.remove('-sdl')
ValueError: list.remove(x): x not in list

Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>

tools/python/xen/xend/image.py

@@ -755,9 +755,8 @@ class HVMImageHandler(ImageHandler):
         if not self.display :
             self.display = ''
 
-        store_dmargs = self.dmargs[:]
-        store_dmargs.remove('-sdl')
-        store_dmargs.remove('-disable-opengl')
+        store_dmargs = [ x for x in self.dmargs
+                         if x not in ['-sdl', '-disable-opengl'] ]
         try :
             midx = store_dmargs.index('-monitor')
             store_dmargs[midx + 1] = 'pty'