Use a button to destroy pages from the edit page

We were already using buttons to destroy pages from the pages index.

As mentioned in commits 5311daadf and bb958daf0, using links combined
with JavaScript to generate POST (or, in this case, DELETE) requests to
the server has a few issues.

app/assets/stylesheets/admin.scss

@@ -511,9 +511,13 @@ code {
   flex-wrap: wrap;
 
   a,
-  button {
+  button,
+  form {
     margin-#{$global-left}: auto;
+  }
 
+  a,
+  button {
     &:not(.delete) {
       @include regular-button;
       margin-#{$global-left}: auto;

app/components/admin/site_customization/pages/edit_component.html.erb

@@ -2,7 +2,13 @@
 <%= back_link_to admin_site_customization_pages_path %>
 
 <%= header do %>
-  <%= link_to t("admin.site_customization.pages.index.delete"), admin_site_customization_page_path(page), method: :delete, class: "delete" %>
+  <%= render Admin::ActionComponent.new(
+    :destroy,
+    @page,
+    text: t("admin.site_customization.pages.index.delete"),
+    method: :delete,
+    class: "delete"
+  ) %>
 <% end %>
 
 <%= render "form" %>

spec/system/admin/site_customization/pages_spec.rb

@@ -93,7 +93,7 @@ describe "Admin custom pages", :admin do
     custom_page = create(:site_customization_page, title: "An example custom page")
     visit edit_admin_site_customization_page_path(custom_page)
 
-    click_link "Delete page"
+    click_button "Delete page"
 
     expect(page).not_to have_content "An example custom page"
     expect(page).not_to have_content "example-page"