Bug 1511536: problem with deleting blocks when edit page first loads

The problem is due to the scope of the blockinstanceId variable being
outside of the click handler function, which inadvertently makes it
into a sort of static variable shared by all of the delete buttons.

So the solution is to use a locally-scoped blockinstanceId button
inside the click handler method.

Change-Id: I3e8ffac31cc869c545e85c5f53c3e710e2e71243
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Signed-off-by: Aaron Wells <aaronw@catalyst.net.nz>