Update out-of-date comment in vacuumlazy.c

Commit 15c121b3 seems to have
overlooked the need to trim this part of the comment.

Pavan Deolasee

Discussion: http://postgr.es/m/CABOikdPq_9+cWRNZ0RLKTwuZyj=uL85X=Usifa-CbPee1ZCM5A@mail.gmail.com