general: Remove help-related code

Our help documents are unfinished, and we shouldn't ship
unfinished documentation in our initial release.

We can revert this commit when we're ready to write the
documents properly.

Part-of: <https://gitlab.gnome.org/Incubator/loupe/-/merge_requests/156>

help/C/index.page

@@ -1,19 +0,0 @@
-<page xmlns="http://projectmallard.org/1.0/"
-      type="guide" style="task"
-      xmlns:its="http://www.w3.org/2005/11/its"
-      id="index">
-
-  <info>
-    <desc>Help for Loupe.</desc>
-    <title type='link' role="trail"><media its:translate="no" type="image" src="figures/org.gnome.eog-symbolic.svg"/></title>
-    <title type='link'>Loupe</title>
-    <title type='text'>Loupe</title>
-    <credit type="author copyright">
-      <name>Christopher Davis</name>
-      <email>christopherdavis@gnome.org</email>
-      <years>2020</years>
-    </credit>
-  </info>
-
-<title>Loupe</title>
-</page>

help/meson.build

@@ -1,8 +0,0 @@
-sources = [
-  'index.page'
-]
-
-gnome.yelp(
-  meson.project_name(),
-  sources: sources,
-)