Remove empty libraries directory

In commit 067d7e9 (Delete builtin libraries sources) all the libraries
in there were removed, since they are all now automatically downloaded
during the build. To keep the repository clean, remove the empty
directory as well as the build rule that was used to copy libraries from
this (now empty) directory into the build result.

Author: matthijskooijman

build/build.xml

@@ -237,10 +237,6 @@
 
   <!-- copy library folder -->
   <target name="assemble-libraries" unless="light_bundle">
-    <copy todir="${target.path}/libraries">
-      <fileset dir="../libraries"/>
-    </copy>
-
     <download-library name="Ethernet" version="2.0.0"/>
     <download-library name="GSM" version="1.0.6"/>
     <download-library name="Stepper" version="1.1.3"/>