Remove empty substantive subsections from errata pages (#4516)

Based on an earlier errata discussion with Mike, Alastair, and Bruce.

- [2.1
errata](https://deploy-preview-4516--wcag2.netlify.app/errata/21#since-current)
- [2.2
errata](https://deploy-preview-4516--wcag2.netlify.app/errata/22#since-current)

Co-authored-by: Mike Gower <[email protected]>

Author: kfranqueiro

errata/21.html

@@ -42,10 +42,6 @@ <h2>Table of Contents</h2>
     {%- assign trUrl = "https://www.w3.org/TR/WCAG21/" -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">Current Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata have been recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>
@@ -81,10 +77,6 @@ <h3>Editorial Errata</h3>
     {%- endcapture -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">{{ trDate | date: "%d %B %Y" }} Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata have been recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>
@@ -126,10 +118,6 @@ <h3>Editorial Errata</h3>
     {%- endcapture -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">{{ trDate | date: "%d %B %Y" }} Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata have been recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>
@@ -149,10 +137,6 @@ <h3>Editorial Errata</h3>
     {%- endcapture -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">{{ trDate | date: "%d %B %Y" }} Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata have been recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>

errata/22.html

@@ -42,10 +42,6 @@ <h2>Table of Contents</h2>
     {%- assign trUrl = "https://www.w3.org/TR/WCAG22/" -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">Current Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>
@@ -86,10 +82,6 @@ <h3>Editorial Errata</h3>
     {%- endcapture -%}
     <section id="since-{{ trDate }}">
       <h2>Errata since <a href="{{ trUrl }}">{{ trDate | date: "%d %B %Y" }} Publication</a></h2>
-      <section id="substantive-{{ trDate }}">
-        <h3>Substantive Errata</h3>
-        <p>No substantive errata have been recorded at present.</p>
-      </section>
       <section id="editorial-{{ trDate }}">
         <h3>Editorial Errata</h3>
         <ul>