rabbit_feature_flags: Remove pre-3.7.x error messages

They were useful to diagnose failures when upgrading from e.g. 3.6.x to
3.8.x, but this is no longer supported. Therefore, drop this part of the
code.

Author: dumbbell

deps/rabbit/src/rabbit_feature_flags.erl

@@ -1176,15 +1176,6 @@ does_node_support(Node, FeatureNames, Timeout) ->
                     Node, is_supported_locally, [FeatureNames], Timeout)
           end,
     case Ret of
-        {error, pre_feature_flags_rabbitmq} ->
-            %% See run_feature_flags_mod_on_remote_node/4 for
-            %% an explanation why we consider this node a 3.7.x
-            %% pre-feature-flags node.
-            rabbit_log_feature_flags:debug(
-              "Feature flags: no feature flags support on node `~ts`, "
-              "consider the feature flags unsupported: ~tp",
-              [Node, FeatureNames]),
-            false;
         {error, Reason} ->
             rabbit_log_feature_flags:error(
               "Feature flags: error while querying `~tp` support on "

deps/rabbit/src/rabbit_ff_controller.erl

@@ -1084,25 +1084,6 @@ this_node_first(Nodes) ->
 
 rpc_call(Node, Module, Function, Args, Timeout) ->
     case rpc:call(Node, Module, Function, Args, Timeout) of
-        {badrpc, {'EXIT',
-                  {undef,
-                   [{rabbit_feature_flags, Function, Args, []}
-                    | _]}}} ->
-            %% If rabbit_feature_flags:Function() is undefined
-            %% on the remote node, we consider it to be a 3.7.x
-            %% pre-feature-flags node.
-            %%
-            %% Theoretically, it could be an older version (3.6.x and
-            %% older). But the RabbitMQ version consistency check
-            %% (rabbit_misc:version_minor_equivalent/2) called from
-            %% rabbit_mnesia:check_rabbit_consistency/2 already blocked
-            %% this situation from happening before we reach this point.
-            ?LOG_DEBUG(
-               "Feature flags: ~ts:~ts~tp unavailable on node `~ts`: "
-               "assuming it is a RabbitMQ 3.7.x pre-feature-flags node",
-               [Module, Function, Args, Node],
-               #{domain => ?RMQLOG_DOMAIN_FEAT_FLAGS}),
-            {error, pre_feature_flags_rabbitmq};
         {badrpc, Reason} = Error ->
             ?LOG_ERROR(
                "Feature flags: error while running:~n"