Deprecate passing a String to render_elements from_page

Passing a String to `render_elements` `from_page` option will
not be supported anymore in Alchemy 6. Please load the page
beforehand and pass it as object instead.

lib/alchemy/elements_finder.rb

@@ -81,6 +81,9 @@ def get_page(page_or_layout)
       when Alchemy::Page
         page_or_layout
       when String
+        Alchemy::Deprecation.warn "Passing a String as `from_page` option to " \
+          "`render_elements` is deprecated and will be removed with Alchemy 6.0. " \
+          "Please load the page beforehand and pass it as an object instead."
         Alchemy::Page.find_by(
           language: Alchemy::Language.current,
           page_layout: page_or_layout,

spec/libraries/elements_finder_spec.rb

@@ -149,25 +149,5 @@
         end
       end
     end
-
-    context "with page layout name given as options[:from_page]" do
-      subject { finder.elements(page: "standard") }
-
-      let(:page) { create(:alchemy_page, :public, page_layout: "standard") }
-      let!(:visible_element) { create(:alchemy_element, public: true, page: page) }
-      let!(:hidden_element) { create(:alchemy_element, public: false, page: page) }
-
-      it "returns all public elements from page with given page layout" do
-        is_expected.to eq([visible_element])
-      end
-
-      context "that is not found" do
-        subject { finder.elements(page: "foobaz") }
-
-        it "returns empty active record relation" do
-          is_expected.to eq(Alchemy::Element.none)
-        end
-      end
-    end
   end
 end