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}
diff --git a/webrtc/common_audio/audio_converter.cc b/webrtc/common_audio/audio_converter.cc
index d1dcacd..231ba88 100644
--- a/webrtc/common_audio/audio_converter.cc
+++ b/webrtc/common_audio/audio_converter.cc
@@ -109,7 +109,7 @@
  public:
   CompositionConverter(std::vector<std::unique_ptr<AudioConverter>> converters)
       : converters_(std::move(converters)) {
-    RTC_CHECK_GE(converters_.size(), 2u);
+    RTC_CHECK_GE(converters_.size(), 2);
     // We need an intermediate buffer after every converter.
     for (auto it = converters_.begin(); it != converters_.end() - 1; ++it)
       buffers_.push_back(