help: Drop Keyboard Shortcuts page

We don't need it any more since we have a Keyboard Shortcuts overlay.
And there were no complaints about removing the page.

help/C/shortcuts.page

@@ -1,51 +0,0 @@
-<page xmlns="http://projectmallard.org/1.0/"
-      type="topic" style="task"
-      id="shortcuts">
-  <info>
-
-<!--
-Let's not include Keyboard Shortcuts here for now.
-See https://mail.gnome.org/archives/desktop-devel-list/2018-December/msg00024.html
-    <link type="guide" xref="index#advanced" />
--->
-
-    <revision version="0.1" date="2012-01-15" status="review"/>
-
-    <credit type="author copyright">
-      <name>Brian Grohe</name>
-      <email>grohe43@gmail.com</email>
-      <years>2012</years>
-    </credit>
-
-    <desc></desc>
-  </info>
-
-  <title>Keyboard shortcuts</title>
-     <table frame="all" rules="cols" shade="rows">
-       <tr>
-         <td><p>New game</p></td>
-         <td><p><keyseq><key>Ctrl</key><key>N</key></keyseq></p></td>
-       </tr>
-       <tr>
-         <td><p>Open</p></td>
-         <td><p><keyseq><key>Ctrl</key><key>O</key></keyseq></p></td>
-       </tr>
-       <tr>
-         <td><p>Save</p></td>
-         <td><p><keyseq><key>Ctrl</key><key>S</key></keyseq></p></td>
-       </tr>
-       <tr>
-         <td><p>Undo Move</p></td>
-         <td><p><keyseq><key>Ctrl</key><key>Z</key></keyseq></p></td>
-       </tr>
-       <tr>
-          <td><p>Help</p></td>
-          <td><p><key>F1</key></p></td>
-        </tr>
-        <tr>
-          <td><p>Quit</p></td>
-          <td><p><keyseq><key>Ctrl</key><key>Q</key></keyseq></p></td>
-        </tr>
-      </table>
-
-</page>

help/meson.build

@@ -10,7 +10,6 @@ help_sources = [
   'play.page',
   'rules.page',
   'save-resume.page',
-  'shortcuts.page',
   'timer.page',
   'translate.page',
 ]