bug#65190: 30.0.50; Emacs doesn't build with `--with-mailutils` by default when mailutils is installed on macOS

[Mou Tong]

After the android branch merged, the file `configure.ac`'s section about
`mailutils` changed.

When I build Emacs on macOS with `./configure`, cli will remind me:

```
configure: WARNING: This configuration installs a 'movemail' program
that does not retrieve POP3 email.  By default, Emacs 25 and earlier
installed a 'movemail' program that retrieved POP3 email via only
insecure channels, a practice that is no longer recommended but that
you can continue to support by using './configure --with-pop'.
configure: You might want to use './configure --with-mailutils'.
```

I have installed mailtuils by homebrew (a package manager on macOS), and
it works fine before the android branch got merged.

I guess the problem occurs in this line

https://git.savannah.gnu.org/cgit/emacs.git/tree/configure.ac?id=e1d08e9e11d2bd5e93c8ae4ea4a8e27129b316cb#n349

But I don't know how to fix this :(