Let `package-install-selected-packages' install packages without asking for confirmation.

[Hongyi Zhao <hongyi.zhao@gmail.com>]

I use the following init file:

```
;https://emacs.stackexchange.com/questions/34180/how-can-i-script-emacs-to-install-packages-from-list
;https://stackoverflow.com/questions/10092322/how-to-automatically-install-emacs-packages-by-specifying-a-list-of-package-name
(require 'package)
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
(package-initialize)

(setq package-selected-packages
      '(company
        async))
(package-install-selected-packages)


(unless package-archive-contents
  (package-refresh-contents))
(package-install-selected-packages t)
```

But when I start Emacs, it still asks me to confirm the installation
of the packages. See the following info shown in minibuffer:

Packages to install: 2 (company async), proceed? (y or n)

As you can see, I've set the `(package-install-selected-packages t)'
option. So, how to let `package-install-selected-packages' install
packages without asking for confirmation.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province