Stop warning in ENV.x11

It has been long enough since `depends_on :x11` was introduced that we
can make it the caller's responsibility to ensure X11 is present before
invoking ENV.x11, so stop outputting a warning.

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

Library/Homebrew/extend/ENV.rb

@@ -246,12 +246,7 @@ module HomebrewEnvExtension
     end
   end
 
-  def x11 silent=false
-    unless MacOS::X11.installed?
-      opoo "You do not have X11 installed, this formula may not build." unless silent
-      return
-    end
-
+  def x11
     # There are some config scripts here that should go in the PATH
     prepend 'PATH', MacOS::X11.bin, ':'
 

Library/Homebrew/test/test_ENV.rb

@@ -15,7 +15,6 @@ class EnvironmentTests < Test::Unit::TestCase
     ENV.minimal_optimization
     ENV.no_optimization
     ENV.libxml2
-    ENV.x11 true
     ENV.enable_warnings
     assert !ENV.cc.empty?
     assert !ENV.cxx.empty?