Remove runescape-api and mixins

This code is used by internal tooling to build the client patch, which
is already closed source, and is not directly shipped as a dependency.

Outside contributions to it are rare due to the lack of build tools, and it is
primarily being abused by others. As such, I no longer wish to release
further changes to it under BSD-2.

README.md

@@ -11,8 +11,6 @@ If you have any questions, please join our IRC channel on [irc.rizon.net #runeli
 - [http-api](http-api/src/main/java/net/runelite/http/api) - API for api.runelite.net
 - [http-service](http-service/src/main/java/net/runelite/http/service) - Service for api.runelite.net
 - [runelite-api](runelite-api/src/main/java/net/runelite/api) - RuneLite API, interfaces for accessing the client
-- [runelite-mixins](runelite-mixins/src/main/java/net/runelite) - Mixins which are injected into the injected client's classes
-- [runescape-api](runescape-api/src/main/java/net/runelite) - Mappings correspond to these interfaces, runelite-api is a subset of this
 - [runelite-client](runelite-client/src/main/java/net/runelite/client) - Game client with plugins
 
 ## Usage