Minor improvement: Remove observer_cli from CLI escritps

[gomoripeti]

Proposed Changes

observer_cli (and its dependency recon) was declared as a dependency of rabbitmq_cli and as a consequence included in all escritps. However the major part of observer_cli runs in the broker. The cli side only used observer_cli:rpc_start/2 which is just an rpc call into the target node.

By using common rpc call we can remove observer_cli and recon from the escripts. This can be considered a minor improvement based on the philosophy "simpler is better".

As an additional benefit auto-completing functions of the recon app now works in rabbitmq-diagnostics remote_shell.
(eg. recon:proc_c<TAB>) This was my main motivation for this change.

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