Remove leftovers in TelnetServer sample.

[slaff]

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[what-the-diff]

PR Summary

• Removal of specific Command Handler
  The developer has taken out the 'CommandProcessing::enable(commandHandler, Serial);' section from the code. This means that they have eliminated a part of the code which was used to process commands and perform certain functions automatically, using a specific commandHandler and the Serial interface.

• Inclusion of General Command Handlers
  They have included a new, more generalized 'command handlers' function, '// set command handlers'. This enables the software to process different types of commands more effectively, possibly to enable a wider range of functionality, without being limited by the previous specific command handler. This can potentially improve the software's flexibility and adaptability to various tasks or situations.