OwnIdentity.deleteWithoutCommit(): Use mInsertURIString

- The upgradeDatabaseFormatVersion5() which is mentioned in the added
comment will be added in a following commit.
OwnIdentity.startupDatabaseIntegrityTest(): Use mInsertURIString

Now not mInsertURIString == null but also mInsertURI != null is an
error since it is replacd by mInsertURIString and thus should always be
null as specified by its  JavaDoc.
OwnIdentity.storeWithoutCommit(): Use mInsertURIString