Remove rabbitmq_stream_prometheus plugin

All these metrics, except publishers & consumers, are handled by
rabbitmq_global_metrics, so we currently have duplicates. As I started
removing these, I realised that tests were written in Java - why not
Erlang? - and they seemed way too complicated for what was needed. After
the new rabbitmq_global_metrics, we are left with 2 metrics, and all the
extra code simply doesn't justify them. I am proposing that we add them to
rabbit_global_counters as gauges. Let's discuss @dcorbacho @acogoluegnes

Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>

BUILD.bazel

@@ -77,7 +77,6 @@ ALL_PLUGINS = [
     "//deps/rabbitmq_stomp:bazel_erlang_lib",
     "//deps/rabbitmq_stream:bazel_erlang_lib",
     "//deps/rabbitmq_stream_management:bazel_erlang_lib",
-    "//deps/rabbitmq_stream_prometheus:bazel_erlang_lib",
     "//deps/rabbitmq_top:bazel_erlang_lib",
     "//deps/rabbitmq_tracing:bazel_erlang_lib",
     "//deps/rabbitmq_trust_store:bazel_erlang_lib",