Disable pdf generation in the `libvorbis` formula.

The pdf generation fails (with a default working MacTeX installation)
while in interactive mode, hanging the `brew install` process.  The HTML
docs are still getting installed.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/libvorbis.rb

@@ -9,8 +9,7 @@ class Libvorbis <Formula
 
   def install
     system "./configure", "--prefix=#{prefix}", "--disable-debug",
-                          "--disable-dependency-tracking",
-                          "--enable-docs"
+                          "--disable-dependency-tracking"
     system "make install"
   end
 end