Remove @proxy from the specification. Deprecate the annotation.

CHANGELOG.md

 ## 1.25.0
 
 ### Language
 * A string in a `part of` declaration may now be used to refer to the library
   this file is part of.
   A library part can now declare its library either as:
   `part of name.of.library;` or as `part of "uriReferenceOfLibrary.dart";`.
   This allows libraries with no library declarations (and therefore no name)
   to have parts, and it allows tools to easily find the library of a part
   file.
@@ skipping 12 matching lines @@
   * Added 'timeout' parameter to 'Socket.connect', 'RawSocket.connect',
     'SecureSocket.connect' and 'RawSecureSocket.connect. If a connection attempt
     takes longer than the duration specified in 'timeout', a 'SocketException'
     will be thrown. Note: if the duration specified in 'timeout' is greater than
     the system level timeout duration, a timeout may occur sooner than specified
     in 'timeout'.
 
 * `dart:core`
   * The `Uri` class now correctly handles paths while running on Node.js on
     Windows.
+  * Deprecated the `proxy` annotation.
 
 * `dart:developer`
   * `Timeline.startSync` and `Timeline.timeSync` now accept an optional
     parameter `flow` of type `Flow`. The `flow` parameter is used to generate
     flow timeline events that are enclosed by the slice described by
     `Timeline.{start,finish}Sync` and `Timeline.timeSync`.
 
 ### Dart VM
 * Support for MIPS has been removed.
 
@@ skipping 2139 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.