Remove defined check when requiring from string_ext

Author: janlelis

lib/unicode/display_width/string_ext.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "../display_width" unless defined? Unicode::DisplayWidth
+require_relative "../display_width"
 
 class String
   def display_width(ambiguous = 1, overwrite = {}, options = {})