refactor: Remove VimL function test_autochdir()

- Eliminate global test_autochdir.
- Eliminate VimL function test_autochdir()
- Use a lua test instead. Fails correctly after reverting
  0c43479979 / vim-patch:7.4.2015.

src/nvim/buffer.c

@@ -1330,7 +1330,7 @@ void enter_buffer(buf_T *buf)
 void do_autochdir(void)
 {
   if (p_acd) {
-    if ((starting == 0 || test_autochdir)
+    if (starting == 0
         && curbuf->b_ffname != NULL
         && vim_chdirfile(curbuf->b_ffname) == OK) {
       shorten_fnames(true);

src/nvim/eval.c

@@ -17159,12 +17159,6 @@ static void f_tempname(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   rettv->vval.v_string = vim_tempname();
 }
 
-// "test_autochdir()" function
-static void f_test_autochdir(typval_T *argvars, typval_T *rettv, FunPtr fptr)
-{
-  test_autochdir = true;
-}
-
 // "termopen(cmd[, cwd])" function
 static void f_termopen(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {

src/nvim/eval.lua

@@ -301,7 +301,6 @@ return {
     tan={args=1, func="float_op_wrapper", data="&tan"},
     tanh={args=1, func="float_op_wrapper", data="&tanh"},
     tempname={},
-    test_autochdir={},
     termopen={args={1, 2}},
     test={args=1},
     timer_start={args={2,3}},

src/nvim/globals.h

@@ -641,8 +641,6 @@ EXTERN volatile int full_screen INIT(= FALSE);
 /* TRUE when doing full-screen output
  * otherwise only writing some messages */
 
-EXTERN int test_autochdir INIT(= false);
-
 EXTERN int restricted INIT(= FALSE);
 // TRUE when started in restricted mode (-Z)
 EXTERN int secure INIT(= FALSE);

src/nvim/testdir/Makefile

@@ -30,7 +30,6 @@ SCRIPTS := \
 # Tests using runtest.vim.vim.
 # Keep test_alot*.res as the last one, sort the others.
 NEW_TESTS = \
-	    test_autochdir.res \
 	    test_bufwintabinfo.res \
 	    test_cmdline.res \
 	    test_cscope.res \

src/nvim/testdir/test_autochdir.vim

@@ -1,17 +0,0 @@
-" Test 'autochdir' behavior
-
-if !exists("+autochdir")
-  finish
-endif
-
-func Test_set_filename()
-  call test_autochdir()
-  set acd
-  new
-  w samples/Xtest
-  call assert_equal("Xtest", expand('%'))
-  call assert_equal("samples", substitute(getcwd(), '.*/\(\k*\)', '\1', ''))
-  bwipe!
-  set noacd
-  call delete('samples/Xtest')
-endfunc