RTC_[D]CHECK_op: Remove "u" suffix on integer constants

There's no longer any need to make the two arguments have the same
signedness, so we can drop the "u" suffix on literal integer
arguments.

NOPRESUBMIT=true
BUG=webrtc:6645

Review-Url: https://codereview.webrtc.org/2535593002
Cr-Commit-Position: refs/heads/master@{#15280}

webrtc/modules/rtp_rtcp/source/rtcp_packet/bye.cc

@@ -101,7 +101,7 @@ bool Bye::Create(uint8_t* packet,
     *index += reason_length;
     // Add padding bytes if needed.
     size_t bytes_to_pad = index_end - *index;
-    RTC_DCHECK_LE(bytes_to_pad, 3u);
+    RTC_DCHECK_LE(bytes_to_pad, 3);
     if (bytes_to_pad > 0) {
       memset(&packet[*index], 0, bytes_to_pad);
       *index += bytes_to_pad;