Delete or update left-over ASSERT use and comments.

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index 51882da0f9b01facb2fd2ee0d7115bdf8d18bb09..16b010015d53de91c8d419e76c682786675c59f1 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -665,12 +665,6 @@ rtc_static_library("rtc_base") {
       "unixfilesystem.cc",
       "unixfilesystem.h",
     ]
-    if (is_debug) {
-      # The Chromium build/common.gypi defines this for all posix
-      # _except_ for ios & mac.  We want it there as well, e.g.
-      # because ASSERT and friends trigger off of it.
-      defines += [ "_DEBUG" ]
-    }

[kwiberg-webrtc, 2017/01/23 12:25:14]

Curiously, _DEBUG seems to be a Windows thing, not a posix thing as implied by
this code: http://stackoverflow.com/questions/2290509/debug-vs-ndebug

I'm not sure if we need it or not. Did we use it before? E.g. was ASSERT defined
in terms of _DEBUG as the comment claims?

[nisse-webrtc, 2017/01/23 12:53:03]

I've search history, _DEBUG was used in lots of places before cl
https://codereview.webrtc.org/1429513004 (but not for ASSERT, as far as I see).
More recently, it was used in peerconnection_unittests.cc, and that use deleted
in cl https://codereview.webrtc.org/1837393002

   }
 
   if (is_nacl) {