patch 8.1.0711: test files still use function!

Problem:    Test files still use function!.
Solution:   Remove the exclamation mark.  Fix overwriting a function.
diff --git a/src/testdir/test_window_cmd.vim b/src/testdir/test_window_cmd.vim
index 0980493..587ae23 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -578,13 +578,13 @@
   only
 endfunc
 
-function! Fun_RenewFile()
+func Fun_RenewFile()
   sleep 2
   silent execute '!echo "1" > tmp.txt'
   sp
   wincmd p
   edit! tmp.txt
-endfunction
+endfunc
 
 func Test_window_prevwin()
   " Can we make this work on MS-Windows?