flags/appeals: replace is_resolved flag with statuses.

Replace references to the `is_resolved` field with the `status` field.
Post flags were marked as resolved when a post was approved (but not
when the post was deleted because it went unapproved). The status field
supercedes the resolved field.

test/factories/post_flag.rb

@@ -3,6 +3,5 @@ FactoryBot.define do
     creator
     post { build(:post, is_flagged: true) }
     reason {"xxx"}
-    is_resolved {false}
   end
 end

test/functional/post_events_controller_test.rb

@@ -8,10 +8,10 @@ class PostEventsControllerTest < ActionDispatch::IntegrationTest
     end
 
     as(@user) do
-      @post = create(:post)
-      @post.flag!("aaa")
+      @post = create(:post, is_flagged: true)
+      create(:post_flag, post: @post, status: :rejected)
       @post.update(is_deleted: true)
-      create(:post_appeal, post: @post)
+      create(:post_appeal, post: @post, status: :succeeded)
       @post.approve!(@mod)
     end
   end
@@ -38,9 +38,5 @@ class PostEventsControllerTest < ActionDispatch::IntegrationTest
     should "render" do
       assert_not_nil(@appeal)
     end
-
-    should "return is_resolved correctly" do
-      assert_equal(false, @appeal["is_resolved"])
-    end
   end
 end