Remove obsolete doctor check

We don't support 10.5 anymore, and tigerbrew doesn't have this check
anymore, either.

Library/Homebrew/cmd/doctor.rb

@@ -1001,23 +1001,6 @@ def check_git_status
   end
 end
 
-def check_git_ssl_verify
-  if MacOS.version <= :leopard && !ENV['GIT_SSL_NO_VERIFY'] then <<-EOS.undent
-    The version of libcurl provided with Mac OS X #{MacOS.version} has outdated
-    SSL certificates.
-
-    This can cause problems when running Homebrew commands that use Git to
-    fetch over HTTPS, e.g. `brew update` or installing formulae that perform
-    Git checkouts.
-
-    You can force Git to ignore these errors:
-      export GIT_SSL_NO_VERIFY=1
-    or
-      git config --global http.sslVerify false
-    EOS
-  end
-end
-
 def check_for_enthought_python
   if which "enpkg" then <<-EOS.undent
     Enthought Python was found in your PATH.