patch 9.0.0767: 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_trycatch.vim b/src/testdir/test_trycatch.vim
index 28cd39f..9d62084 100644
--- a/src/testdir/test_trycatch.vim
+++ b/src/testdir/test_trycatch.vim
@@ -1975,7 +1975,7 @@
 endfunc
 
 func Test_reload_in_try_catch()
-  call writefile(['x'], 'Xreload')
+  call writefile(['x'], 'Xreload', 'D')
   set autoread
   edit Xreload
   tabnew
@@ -1995,7 +1995,6 @@
   autocmd! ReLoad
   set noautoread
   bwipe! Xreload
-  call delete('Xreload')
 endfunc
 
 " Test for errors with :catch, :throw, :finally                            {{{1
@@ -2306,10 +2305,8 @@
       call s:main()
       call assert_equal('yes', s:caught)
   END
-  call writefile(lines, 'XtestThrow')
+  call writefile(lines, 'XtestThrow', 'D')
   source XtestThrow
-
-  call delete('XtestThrow')
 endfunc
 
 func ThisWillFail()
@@ -2325,13 +2322,11 @@
       for l in []
     finally
   END
-  call writefile(lines, 'XtestCatchAndFinally')
+  call writefile(lines, 'XtestCatchAndFinally', 'D')
   try
     source XtestCatchAndFinally
   catch /E600:/
   endtry
-
-  call delete('XtestCatchAndFinally')
 endfunc
 
 " This was causing an illegal memory access
@@ -2345,13 +2340,11 @@
       if
       endtry
   END
-  call writefile(lines, 'XtestEndtry')
+  call writefile(lines, 'XtestEndtry', 'D')
   try
     source XtestEndtry
   catch /E171:/
   endtry
-
-  call delete('XtestEndtry')
 endfunc
 
 " Modeline								    {{{1