skins: replace {js,css}.template with actual files. Simplify startup scripts.

Currently, an Etherpad skin requires the existence of 6 files:
- index.{css,js}
- pad.{css,js}
- timeslider.{css,js}

In the default empty skin (in static/custom), there were 2 small placeholders
({js,css}.template) to be copied in place by the startup script in case no skin
was in use.

Now that we are moving to multiple directories (see #3471) we can simply commit
the example files and remove the copying code from the startup script.

bin/installDeps.sh

@@ -143,17 +143,4 @@ fi
 echo "Clearing minified cache..."
 rm -f var/minified*
 
-echo "Ensure custom css/js files are created..."
-
-for f in "index" "pad" "timeslider"
-do
-  if [ ! -f "src/static/custom/$f.js" ]; then
-    cp "src/static/custom/js.template" "src/static/custom/$f.js" || exit 1
-  fi
-
-  if [ ! -f "src/static/custom/$f.css" ]; then
-    cp "src/static/custom/css.template" "src/static/custom/$f.css" || exit 1
-  fi
-done
-
 exit 0