Remove theme_option

crates/mdbook-html/src/html_handlebars/hbs_renderer.rs

@@ -271,8 +271,6 @@ impl HtmlHandlebars {
                 no_section_label: html_config.no_section_label,
             }),
         );
-        // TODO: remove theme_option in 0.5, it is not needed.
-        handlebars.register_helper("theme_option", Box::new(helpers::theme::theme_option));
     }
 
     fn emit_redirects(
@@ -558,7 +556,6 @@ fn make_data(
         );
     }
 
-    // TODO: remove default_theme in 0.5, it is not needed.
     let default_theme = match html_config.default_theme {
         Some(ref theme) => theme.to_lowercase(),
         None => "light".to_string(),

crates/mdbook-html/src/html_handlebars/helpers/mod.rs

@@ -1,3 +1,2 @@
 pub(crate) mod resources;
-pub(crate) mod theme;
 pub(crate) mod toc;

crates/mdbook-html/src/html_handlebars/helpers/resources.rs

@@ -23,7 +23,7 @@ impl HelperDef for ResourceHelper {
     ) -> Result<(), RenderError> {
         let param = h.param(0).and_then(|v| v.value().as_str()).ok_or_else(|| {
             RenderErrorReason::Other(
-                "Param 0 with String type is required for theme_option helper.".to_owned(),
+                "Param 0 with String type is required for resource helper.".to_owned(),
             )
         })?;