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_indent.vim b/src/testdir/test_indent.vim
index 97c44b8..290855e 100644
--- a/src/testdir/test_indent.vim
+++ b/src/testdir/test_indent.vim
@@ -161,7 +161,7 @@
   func GetIndent()
     return line('.') * 2
   endfunc
-  call writefile(['# vim: indentexpr=GetIndent()'], 'Xmlfile.txt')
+  call writefile(['# vim: indentexpr=GetIndent()'], 'Xmlfile.txt', 'D')
   set modelineexpr
   new Xmlfile.txt
   call assert_equal('GetIndent()', &indentexpr)
@@ -172,7 +172,6 @@
   delfunc GetIndent
   let &modeline = modeline
   close!
-  call delete('Xmlfile.txt')
 endfunc
 
 func Test_indent_func_with_gq()