patch 9.0.0625: too many delete() calls in tests

Problem:    Too many delete() calls in tests.
Solution:   Use deferred delete where possible.
diff --git a/src/testdir/test_jumplist.vim b/src/testdir/test_jumplist.vim
index 054fda0..4b5e321 100644
--- a/src/testdir/test_jumplist.vim
+++ b/src/testdir/test_jumplist.vim
@@ -15,7 +15,7 @@
   for i in range(1, 100)
     call add(lines, "Line " . i)
   endfor
-  call writefile(lines, "Xtest")
+  call writefile(lines, "Xtest", 'D')
 
   " Jump around and create a jump list
   edit Xtest
@@ -57,8 +57,6 @@
   clearjumps
   call test_garbagecollect_now()
   call assert_equal(4, l[1])
-
-  call delete("Xtest")
 endfunc
 
 func Test_jumplist_invalid()