gfortran: remove dependency on nonexistent "expect" formula

expect is already installed on Mac OS, and there is no such formula.

Closes Homebrew/homebrew#16730.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/gfortran.rb

@@ -23,7 +23,6 @@ class Gfortran < Formula
 
   begin
     depends_on 'dejagnu'
-    depends_on 'expect'
   end if build.include? 'check'  # http://gcc.gnu.org/install/test.html
 
   fails_with :clang do