docs: fix first heading rendering as paragraph on two template guides

The ng-container and binding template guide files each began with a
UTF-8 BOM (EF BB BF) before the leading `#`. The docs markdown parser
only promotes `#` to an H1 when it is the first character on the line,
so the BOM demoted the title to paragraph text (`<p># ...</p>`) and the
standard docs header (breadcrumbs, page title, edit button) never
rendered.

Stripping the BOM restores `#` as the first character, so both pages
now generate the proper `<header class="docs-header">` block. Verified
by rebuilding //adev/src/content/guide/templates:templates and
inspecting the generated HTML.

Fixes #69889

adev/src/content/guide/templates/binding.md

@@ -1,4 +1,4 @@
-# Binding dynamic text, properties and attributes
+# Binding dynamic text, properties and attributes
 
 In Angular, a **binding** creates a dynamic connection between a component's template and its data. This connection ensures that changes to the component's data automatically update the rendered template.
 

adev/src/content/guide/templates/ng-container.md

@@ -1,4 +1,4 @@
-# Grouping elements with ng-container
+# Grouping elements with ng-container
 
 `<ng-container>` is a special element in Angular that groups multiple elements together or marks a location in a template without rendering a real element in the DOM.