umh: Stop calling do_execve_file

With the user mode driver code changed to not set subprocess_info.file
there are no more users of subproces_info.file. Remove this field
from struct subprocess_info and remove the only user in
call_usermodehelper_exec_async that would call do_execve_file instead
of do_execve if file was set.

v1: https://lkml.kernel.org/r/[e-mail]
v2: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Acked-by: Alexei Starovoitov <[e-mail]>
Tested-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: "Eric W. Biederman" <[e-mail]>

include/linux/umh.h

···
 	const char *path;
 	char **argv;
 	char **envp;
-	struct file *file;
 	int wait;
 	int retval;
 	int (*init)(struct subprocess_info *info, struct cred *new);

kernel/umh.c

···
 
 	commit_creds(new);
 
-	if (sub_info->file)
-		retval = do_execve_file(sub_info->file,
-					sub_info->argv, sub_info->envp);
-	else
-		retval = do_execve(getname_kernel(sub_info->path),
-				   (const char __user *const __user *)sub_info->argv,
-				   (const char __user *const __user *)sub_info->envp);
+	retval = do_execve(getname_kernel(sub_info->path),
+			   (const char __user *const __user *)sub_info->argv,
+			   (const char __user *const __user *)sub_info->envp);
 out:
 	sub_info->retval = retval;
 	/*