Revert "Ensure the output dir exists in Generator::Header#save_as"

This reverts commit a23a07e49c29b4def57f13160369f175c66cf585.

lib/cocoapods/generator/header.rb

@@ -64,7 +64,6 @@ module Pod
       # @return [void]
       #
       def save_as(path)
-        FileUtils.mkdir_p(path + '..')
         path.open('w') { |header| header.write(generate) }
       end