store/copr: use non-buffered channel for coprocessor response (#35988)

close #35987

store/copr/coprocessor.go

@@ -123,21 +123,7 @@ func (c *CopClient) Send(ctx context.Context, req *kv.Request, variables interfa
 		it.sendRate = util.NewRateLimit(2 * it.concurrency)
 		it.respChan = nil
 	} else {
-		capacity := it.concurrency
-		if enabledRateLimitAction {
-			// The count of cached response in memory is controlled by the capacity of the it.sendRate, not capacity of the respChan.
-			// As the worker will send finCopResponse after each task being handled, we make the capacity of the respCh equals to
-			// 2*it.concurrency to avoid deadlock in the unit test caused by the `MustExec` or `Exec`
-			capacity = it.concurrency * 2
-		}
-		// in paging request, a request will be returned in multi batches,
-		// enlarge the channel size to avoid the request blocked by buffer full.
-		if req.Paging {
-			if capacity < 2048 {
-				capacity = 2048
-			}
-		}
-		it.respChan = make(chan *copResponse, capacity)
+		it.respChan = make(chan *copResponse)
 		it.sendRate = util.NewRateLimit(it.concurrency)
 	}
 	it.actionOnExceed = newRateLimitAction(uint(it.sendRate.GetCapacity()))