Use unf on all versions; native is more than 11x slower

lib/simpleidn.rb

@@ -1,10 +1,6 @@
 require 'simpleidn/version'
 require 'simpleidn/uts46mapping'
-
-# If no known method for normalization is available, load unf to get one
-unless ''.respond_to?(:unicode_normalize) || ''.respond_to?(:to_nfc)
-  require 'unf'
-end
+require 'unf'
 
 module SimpleIDN
   # The ConversionError is raised when an error occurs during a
@@ -227,9 +223,6 @@ def uts46map(str, transitional = false)
     mapped = str.codepoints.map { |cp| UTS64MAPPING.fetch(cp, cp) }
     mapped = mapped.map { |cp| TRANSITIONAL.fetch(cp, cp) } if transitional
     mapped = mapped.flatten.map { |cp| cp.chr(Encoding::UTF_8) }.join(EMPTY)
-
-    # Prefer the internal method if available (e.g. Ruby 2.2 or later)
-    return mapped.unicode_normalize(:nfc) if mapped.respond_to? :unicode_normalize
     mapped.to_nfc
   end