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.

runtime/doc/eval.txt

@@ -2207,7 +2207,6 @@ tagfiles()			List	tags files used
 tan({expr})			Float	tangent of {expr}
 tanh({expr})			Float	hyperbolic tangent of {expr}
 tempname()			String	name for a temporary file
-test_autochdir()		none	enable 'autochdir' during startup
 timer_start({time}, {callback} [, {options}])
 				Number	create a timer
 timer_stop({timer})		none	stop a timer
@@ -7214,10 +7213,6 @@ tempname()					*tempname()* *temp-file-name*
 		For MS-Windows forward slashes are used when the 'shellslash'
 		option is set or when 'shellcmdflag' starts with '-'.
 
-test_autochdir()					*test_autochdir()*
-		Set a flag to enable the effect of 'autochdir' before Vim
-		startup has finished.
-
 termopen({cmd}[, {opts}])			{Nvim} *termopen()*
 		Spawns {cmd} in a new pseudo-terminal session connected
 		to the current buffer.  {cmd} is the same as the one passed to

runtime/doc/usr_41.txt

@@ -904,7 +904,6 @@ Testing:				    *test-functions*
 	assert_true()		assert that an expression is true
 	assert_exception()	assert that a command throws an exception
 	assert_fails()		assert that a function call fails
-	test_autochdir()	enable 'autochdir' during startup
 
 Various:					*various-functions*
 	mode()			get current editing mode