CMS: removal of derived dataset example

* Removes derived dataset example now that event display records have
  been updated in e538be0b9ea0c2bbe1d8b946e5fe6b2f0f2b5fa5.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
CMS: removal of old CMS derived dataset files

* Removes old CMS derived dataset files that were used for demo purposes
  only.  They have been superseded by `cms-eventdisplay-files.xml`.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
README: instructions to load all demo files

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>