patch 8.2.0944: xxd test leaves file behind

Problem:    Xxd test leaves file behind.
Solution:   Delete the file "XXDfile". (Christian Brabandt, closes #6228)
diff --git a/src/testdir/test_xxd.vim b/src/testdir/test_xxd.vim
index 51ee760..37c0c57 100644
--- a/src/testdir/test_xxd.vim
+++ b/src/testdir/test_xxd.vim
@@ -208,7 +208,8 @@
   " -o -offset
 
   %d
-  bw!
+  bwipe!
+  call delete('XXDfile')
 endfunc
 
 " Various ways with wrong arguments that trigger the usage output.