patch 8.1.1638: running tests leaves some files behind

Problem:    Running tests leaves some files behind.
Solution:   Delete the files. (Ozaki Kiichi, closes #4617)
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 3983b57..00cc287 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -1708,6 +1708,7 @@
   let winid = popup_create(bufnr(''), {})
   redraw
   call popup_close(winid)
+  call delete('XsomeFile')
 endfunc
 
 func Test_popupwin_width()