DERBY-6459  Remove Class.forName calls that load JDBC driver from Derby samples/demos

Modified top-level demo.html file to reflect changes to VTI demos.

Patch: DERBY-6459-3.diff


git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1573577 13f79535-47bb-0310-9956-ffa450edef68