docs: remove non directive to stop indexing output code blocks (it doesn't work) (#4461)

This directive seems to have no effect on code blocks: `{
mkdocs-exclude-search }`. Removing it for now.

docs/_scripts/notebook_convert_templates/mdoutput/index.md.j2

@@ -4,21 +4,18 @@
 ```output
 {{ line.rstrip() | strip_ansi }}
 ```
-{ mkdocs-exclude-search }
 {%- endblock traceback_line -%}
 
 {%- block stream -%}
 ```output
 {{ output.text.rstrip() | strip_ansi }}
 ```
-{ mkdocs-exclude-search }
 {%- endblock stream -%}
 
 {%- block data_text scoped -%}
 ```output
 {{ output.data['text/plain'].rstrip() | strip_ansi }}
 ```
-{ mkdocs-exclude-search }
 {%- endblock data_text -%}
 
 {%- block data_html scoped -%}