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-Original-Commit-Position: refs/heads/master@{#15280}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: af476c737fe008a185a99144731fd398e311ba65
89 files changed