Remove obsolete comments and code from prior to
f8f4227976.
XLogReadBufferForRedo() and XLogReadBufferForRedoExtended() only return
BLK_NEEDS_REDO if the record LSN is greater than the page LSN, so
the redo routine doesn't need to do the LSN check again.
Discussion: https://postgr.es/m/
0c37b80e62b1f3007d5a6d1292bd8fa0c275627a.camel@j-davis.com