Replace RTC_DCHECK(false) with RTC_NOTREACHED().

Bulk of changes done using

  git grep -l 'RTC_DCHECK(false)' | \
    xargs sed -i 's/RTC_DCHECK(false)/RTC_NOTREACHED()/'

peerconnection.cc also used RTC_DCHECK(false && "msg") in two places,
which were updated manually.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2623313004
Cr-Commit-Position: refs/heads/master@{#16026}
diff --git a/webrtc/api/statscollector.cc b/webrtc/api/statscollector.cc
index fb6583a..8347424 100644
--- a/webrtc/api/statscollector.cc
+++ b/webrtc/api/statscollector.cc
@@ -351,7 +351,7 @@
   if (candidate_type == cricket::RELAY_PORT_TYPE) {
     return STATSREPORT_RELAY_PORT_TYPE;
   }
-  RTC_DCHECK(false);
+  RTC_NOTREACHED();
   return "unknown";
 }
 
@@ -370,7 +370,7 @@
     case rtc::ADAPTER_TYPE_LOOPBACK:
       return STATSREPORT_ADAPTER_TYPE_LOOPBACK;
     default:
-      RTC_DCHECK(false);
+      RTC_NOTREACHED();
       return "";
   }
 }