Remove libiconv duplicate

Commit ee2c3ab ("Remove spurious libiconv dependencies") pruned all
existing "depends_on 'libiconv'" usages from Homebrew in preparation for
removing the libiconv dupe itself.

Now that is done, and we can remove and blacklist it. It can be obtained
from Homebrew-alt.

Closes Homebrew/homebrew#10464.

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

Library/Homebrew/blacklist.rb

@@ -6,6 +6,11 @@ def blacklisted? name
   when 'libarchive', 'libpcap' then <<-EOS.undent
     Apple distributes #{name} with OS X, you can find it in /usr/lib.
     EOS
+  when 'libiconv' then <<-EOS.undent
+    Apple distributes #{name} with OS X, you can find it in /usr/lib.
+    Some build scripts fail to detect it correctly, please check existing
+    formulae for solutions.
+    EOS
   when 'libxml', 'libxlst' then <<-EOS.undent
     Apple distributes #{name} with OS X, you can find it in /usr/lib.
     However not all build scripts look for these hard enough, so you may need

Library/Homebrew/cmd/doctor.rb

@@ -340,7 +340,7 @@ def check_xcode_prefix
   if prefix.to_s.match(' ')
     <<-EOS.undent
       Xcode is installed to a directory with a space in the name.
-      This will cause some formulae, such as libiconv, to fail to build.
+      This will cause some formulae to fail to build.
     EOS
   end
 end