Simplify reindex_relation's API.

For what seem entirely historical reasons, a bitmask "flags" argument was
recently added to reindex_relation without subsuming its existing boolean
argument into that bitmask.  This seems a bit bizarre, so fold them
together.

src/backend/commands/tablecmds.c

@@ -1080,7 +1080,7 @@ ExecuteTruncate(TruncateStmt *stmt)
 			/*
 			 * Reconstruct the indexes to match, and we're done.
 			 */
-			reindex_relation(heap_relid, true, 0);
+			reindex_relation(heap_relid, REINDEX_REL_PROCESS_TOAST);
 		}
 	}