cleaner: reorganize clean_dir to avoid repeated conditional

Library/Homebrew/cleaner.rb

@@ -74,21 +74,17 @@ class Cleaner
     d.find do |path|
       path.extend(NoisyPathname) if ARGV.verbose?
 
-      if path.directory?
-        # Stop cleaning this subtree if protected
-        Find.prune if @f.skip_clean? path
-      elsif not path.file?
-        # Sanity?
+      Find.prune if @f.skip_clean? path
+
+      if path.symlink? or path.directory?
         next
       elsif path.extname == '.la'
-        # *.la files are stupid
-        path.unlink unless @f.skip_clean? path
+        path.unlink
       elsif path == @f.lib+'charset.alias'
         # Many formulae symlink this file, but it is not strictly needed
-        path.unlink unless @f.skip_clean? path
-      elsif not path.symlink?
-        # Fix permissions
-        clean_file_permissions(path) unless @f.skip_clean? path
+        path.unlink
+      else
+        clean_file_permissions(path)
       end
     end
   end