Delete or update left-over ASSERT use and comments.

BUG=webrtc:6424,webrtc:6323

Review-Url: https://codereview.webrtc.org/2647663002
Cr-Commit-Position: refs/heads/master@{#16215}
diff --git a/webrtc/base/unixfilesystem.h b/webrtc/base/unixfilesystem.h
index e3710ec..d6dfed5 100644
--- a/webrtc/base/unixfilesystem.h
+++ b/webrtc/base/unixfilesystem.h
@@ -44,7 +44,7 @@
   bool DeleteFile(const Pathname& filename) override;
 
   // This will attempt to delete the folder located at 'folder'
-  // It ASSERTs and returns false if you pass it a non-existant folder or a
+  // It DCHECKs and returns false if you pass it a non-existant folder or a
   // plain file.
   bool DeleteEmptyFolder(const Pathname& folder) override;