Remove feature flag dependency

Feature flag 'rabbitmq_4.1.0' does not really depend on
'rabbitmq_4.0.0'. Technically the former can be enabled without the
latter. This commit removes the dependency to troubleshoot mixed version
CI failures stating that feature flags are incompatible.

Author: ansd

deps/rabbit/src/rabbit_core_ff.erl

@@ -209,6 +209,5 @@
 -rabbit_feature_flag(
    {'rabbitmq_4.1.0',
     #{desc          => "Allows rolling upgrades to 4.1.x",
-      stability     => stable,
-      depends_on    => ['rabbitmq_4.0.0']
+      stability     => stable
      }}).