Drop mentions of unused bundler env variables for ruby

Dropped in:
* docker-library/ruby#209
* docker-library/ruby#306

ruby/content.md

@@ -59,6 +59,6 @@ By default, Ruby inherits the locale of the environment in which it is run. For
 
 This image sets several environment variables which change the behavior of Bundler and Gem for running a single application within a container (especially in such a way that the development sources of the application can be bind-mounted inside a container and not have `.bundle` from the host interfere with the proper functionality of the container).
 
-The environment variables we set are canonically listed in the above-linked `Dockerfiles`, but some of them include `GEM_HOME`, `BUNDLE_PATH`, `BUNDLE_BIN`, `BUNDLE_SILENCE_ROOT_WARNING`, and `BUNDLE_APP_CONFIG`.
+The environment variables we set are canonically listed in the above-linked `Dockerfiles`, but some of them include `GEM_HOME`, `BUNDLE_SILENCE_ROOT_WARNING`, and `BUNDLE_APP_CONFIG`.
 
 If these cause issues for your use case (running multiple Ruby applications in a single container, for example), setting them to the empty string *should* be sufficient for undoing their behavior.