Remove alsa-lib dep

Unused directly. Still pulled in transitively (through ffmpeg).

PKGBUILD

@@ -9,7 +9,7 @@ pkgdesc="Standalone web browser from mozilla.org"
 arch=(i686 x86_64)
 license=(MPL GPL LGPL)
 url="https://www.mozilla.org/firefox/"
-depends=(gtk3 gtk2 mozilla-common libxt startup-notification mime-types dbus-glib alsa-lib ffmpeg
+depends=(gtk3 gtk2 mozilla-common libxt startup-notification mime-types dbus-glib ffmpeg
          nss hunspell sqlite ttf-font libpulse icu libvpx)
 makedepends=(unzip zip diffutils python2 yasm mesa imake gconf inetutils xorg-server-xvfb
              autoconf2.13 cargo mercurial)