Revert "Use value_counts instead of tally"

lib/youplot/backends/processing.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module YouPlot
+  # plotting functions.
+  module Backends
+    module Processing
+      module_function
+
+      def count_values(arr, tally: true)
+        # tally was added in Ruby 2.7
+        if tally && Enumerable.method_defined?(:tally)
+          arr.tally
+        else
+          # https://github.com/marcandre/backports
+          arr.each_with_object(Hash.new(0)) { |item, res| res[item] += 1 }
+             .tap { |h| h.default = nil }
+        end
+          .sort { |a, b| a[1] <=> b[1] }
+          .reverse
+          .transpose
+      end
+    end
+  end
+end