DOCSP-44304 - BSON removals (#259)

Author: mongoKart

source/upgrade/v3.txt

@@ -66,6 +66,11 @@ Version 3.0 Breaking Changes
   provides a replacement for a deprecated class, method, or property, the compiler
   messages in v{+last-version-2-number+} will display it.
 
+- The methods, properties, and constructors in the ``MongoDB.Bson`` namespace that were
+  deprecated in previous versions of the driver have been removed. If the driver
+  provides a replacement for a deprecated method, property, or constructor, the compiler
+  messages in v{+last-version-2-number+} will display it.
+
 - The driver drops support for the
   ``MONGODB-CR`` authentication mechanism. To learn more about
   configuring authentication in the {+driver-short+}, see