Remove usage of CHECK_NOTNULL

We want to switch to absl logging instead of glog.  gtest and ceres are
going there, and we already have absl as a dependency.  ABSL doesn't
have CHECK_NOTNULL, and we can move things over in an easier to review
fashion.

Change-Id: Ifd9a11ec34a2357cec43f88dba015db9c28ed2cf
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/network/rawrtc.cc b/aos/network/rawrtc.cc
index e519b2e..6d9bc3d 100644
--- a/aos/network/rawrtc.cc
+++ b/aos/network/rawrtc.cc
@@ -164,8 +164,8 @@
 
 void ScopedDataChannel::Send(struct mbuf *buffer) {
   // TODO(austin): Checking isn't right, handle errors more gracefully.
-  CHECK_RAWRTC(
-      rawrtc_data_channel_send(CHECK_NOTNULL(data_channel_), buffer, true));
+  CHECK(data_channel_ != nullptr);
+  CHECK_RAWRTC(rawrtc_data_channel_send(data_channel_, buffer, true));
 }
 
 uint64_t ScopedDataChannel::buffered_amount() {
@@ -173,8 +173,8 @@
 
   // TODO(austin): Not implemented yet...
   uint64_t result;
-  CHECK_RAWRTC(rawrtc_data_channel_get_buffered_amount(
-      &result, CHECK_NOTNULL(data_channel_)));
+  CHECK(data_channel_ != nullptr);
+  CHECK_RAWRTC(rawrtc_data_channel_get_buffered_amount(&result, data_channel_));
   return result;
 }