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_xxd.vim b/src/testdir/test_xxd.vim
index 6e67893..4538790 100644
--- a/src/testdir/test_xxd.vim
+++ b/src/testdir/test_xxd.vim
@@ -7,17 +7,17 @@
   let s:xxd_cmd = $XXD
 endif
 
-func! PrepareBuffer(lines)
+func PrepareBuffer(lines)
   new
   call append(0, a:lines)
   $d
 endfunc
 
-func! s:Mess(counter)
+func s:Mess(counter)
   return printf("Failed xxd test %d:", a:counter)
 endfunc
 
-func! Test_xxd()
+func Test_xxd()
   call PrepareBuffer(range(1,30))
   set ff=unix
   w XXDfile