Remove redundant setting of tuplesort status

Also add an explanatory comment to match other similar coding within
tuplesort_performsort().

Xing Guo

Reviewed by Richard Guo and Cary Huang
Discussion: https://www.postgresql.org/message-id/CACpMh%2BAQ4GXRKKi9ib2ioUH%2BqwNaSAVbetssJ0tMPfxAWuL2yg%40mail.gmail.com

src/backend/utils/sort/tuplesort.c

@@ -1439,13 +1439,13 @@ tuplesort_performsort(Tuplesortstate *state)
 			 * We were able to accumulate all the tuples required for output
 			 * in memory, using a heap to eliminate excess tuples.  Now we
 			 * have to transform the heap to a properly-sorted array.
+			 * Note that sort_bounded_heap sets the correct state->status.
 			 */
 			sort_bounded_heap(state);
 			state->current = 0;
 			state->eof_reached = false;
 			state->markpos_offset = 0;
 			state->markpos_eof = false;
-			state->status = TSS_SORTEDINMEM;
 			break;
 
 		case TSS_BUILDRUNS: