Remove NOT_USED BufFileTellBlock() from buffile.c

This routine has been marked as NOT_USED since 20ad43b from 2000,
and a patch is planned to switch the logtape/tuplestore APIs to rely on
int64 rather than long for the block nunbers, which is more portable.

Keeping it is more confusing than anything at this stage, so let's get
rid of it entirely.

Thanks for Heikki Linnakangas for the poke on this one.

Discussion: https://postgr.es/m/5047be8c-7ee6-4dd5-af76-6c916c3103b4@iki.fi

Author: michaelpq

src/backend/storage/file/buffile.c

@@ -856,24 +856,6 @@ BufFileSeekBlock(BufFile *file, long blknum)
 					   SEEK_SET);
 }
 
-#ifdef NOT_USED
-/*
- * BufFileTellBlock --- block-oriented tell
- *
- * Any fractional part of a block in the current seek position is ignored.
- */
-long
-BufFileTellBlock(BufFile *file)
-{
-	long		blknum;
-
-	blknum = (file->curOffset + file->pos) / BLCKSZ;
-	blknum += file->curFile * BUFFILE_SEG_SIZE;
-	return blknum;
-}
-
-#endif
-
 /*
  * Return the current fileset based BufFile size.
  *