remove sourceKV from input; xdcr topology service impl

Change-Id: I2773fb1814c9ba014d519fbca390e38d27b122bd
Reviewed-on: http://review.couchbase.org/44033
Tested-by: Yu Sui <ysui68@gmail.com>
Reviewed-by: Xiaomei Zhang <xiaomeizhangatwork@gmail.com>