BUG-509: remove StoreUtils.initialChangeEvent()

This method is unused. Remove it, such that StoreUtils are now
completely independent of org.opendaylight.controller.md.sal, making
them a candidate for move to yang-data-*.

Change-Id: Idf945aee6fd4a80f8ca58fc50bcc997880a60ec0
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-509: remove StoreUtils.initialChangeEvent()"