Fix duplicated consecutive words in comments

Also, fix a comment incorrectly referencing the "streaming read API".
This was renamed to "read stream" shortly before being committed.

Discussion: https://postgr.es/m/CAApHDvq-2Zdqytm_Hf3RmVf0qg5PS9jTFAJ5QTc9xH9pwvwDTA@mail.gmail.com

src/backend/access/heap/heapam.c

@@ -1122,7 +1122,7 @@ heap_beginscan(Relation relation, Snapshot snapshot,
 	/*
 	 * Set up a read stream for sequential scans and TID range scans. This
 	 * should be done after initscan() because initscan() allocates the
-	 * BufferAccessStrategy object passed to the streaming read API.
+	 * BufferAccessStrategy object passed to the read stream API.
 	 */
 	if (scan->rs_base.rs_flags & SO_TYPE_SEQSCAN ||
 		scan->rs_base.rs_flags & SO_TYPE_TIDRANGESCAN)

src/backend/access/heap/vacuumlazy.c

@@ -13,7 +13,7 @@
  * autovacuum_work_mem) memory space to keep track of dead TIDs.  If the
  * TID store is full, we must call lazy_vacuum to vacuum indexes (and to vacuum
  * the pages that we've pruned). This frees up the memory space dedicated to
- * to store dead TIDs.
+ * store dead TIDs.
  *
  * In practice VACUUM will often complete its initial pass over the target
  * heap relation without ever running out of space to store TIDs.  This means