Deleted Android app resources (openhab#1223)

It appears some of the images related to the Android app
are actually maintained in the app's repo rather than here.

A more thorough clean-up of the `addons` folder should probably
be done at some point!

Remove android app page (gathered from external repo) and
replace it with a placeholder.

Signed-off-by: Yannick Schaus <[email protected]>

.vuepress/add_placeholders.rb

@@ -3,23 +3,25 @@
 def add_placeholder_pages()
     puts ">>> Adding placeholder pages for preview"
     [
-        "docs/concepts",
         "docs/configuration/iconsets/classic",
         "docs/configuration/ui/habmin",
         "docs/configuration/ui/habot",
         "docs/configuration/ui/basic",
-        "docs/configuration/ui/basic",
         "docs/configuration/ui/classic",
         "docs/ecosystem/alexa",
         "docs/ecosystem/google-assistant",
         "docs/ecosystem/ifttt",
-        "docs/ecosystem/ifttt",
         "docs/ecosystem/mycroft",
-        "addons/integrations/homekit"
-    ].each { |dir|
-        puts " -> #{dir}/"
-        FileUtils.mkdir_p(dir)
-        File.open("#{dir}/readme.md", "w+") { |f|
+        "addons/integrations/homekit",
+        "docs/apps/android.md"
+    ].each { |path|
+        puts " -> #{path}"
+        page = path
+        if (!(path =~ /\.md/)) then
+            FileUtils.mkdir_p(path)
+            page = path + "/readme.md"
+        end
+        File.open(page, "w+") { |f|
             f.puts "# This content is unavailable"
             f.puts ""
             f.puts "This content is migrated from another repository, and is not included in this preview."

.vuepress/docs-sidebar.js

@@ -86,7 +86,7 @@ module.exports = [
       'configuration/rules-ng',
       'configuration/eclipseiotmarket',
       ['configuration/restdocs', 'REST API'],
-      'apps/android',
+      ['apps/android', 'Android App'],
       'apps/ios',
       'apps/windows',
       ['ecosystem/alexa/', 'Amazon Alexa'],