Remove ExampleGroup#all_examples

Implement the same functionality with ExampleIterator.

src/spectator/example_group.cr

@@ -50,19 +50,6 @@ module Spectator
       end
     end
 
-    # TODO: Remove this method.
-    def all_examples
-      Array(Example).new(example_count).tap do |array|
-        children.each do |child|
-          if child.is_a?(Example)
-            array << child
-          else
-            array.concat(child.as(ExampleGroup).all_examples)
-          end
-        end
-      end
-    end
-
     def finished? : Bool
       children.all?(&.finished?)
     end

src/spectator/includes.cr

@@ -33,3 +33,5 @@ require "./successful_result"
 require "./pending_result"
 require "./failed_result"
 require "./errored_result"
+
+require "./example_iterator"

src/spectator/runner.cr

@@ -5,15 +5,16 @@ module Spectator
     end
 
     def run : Nil
+      iterator = ExampleIterator.new(@group)
       results = [] of Result
       elapsed = Time.measure do
         @formatter.start_suite
-        results = @group.all_examples.map do |example|
+        results = iterator.map do |example|
           @formatter.start_example(example)
           Internals::Harness.run(example).tap do |result|
             @formatter.end_example(result)
           end.as(Result)
-        end
+        end.to_a
       end
       @formatter.end_suite(TestResults.new(results, elapsed))
     end