[build][hexagon] remove unused variable

[cconvey]

Remove unused member variable in the SimulatorRPCChannel class. Fixes a clang warning.

[tvm-bot]

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• cc @mehrdadh _{See #10317 for details}
• Built docs for commit b97d3bc can be found here.

_{Generated by tvm-bot}

[cconvey]

@mehrdadh : Mind reviewing this? It removes a member variable introduced by one of your PRs (#11065). Looks like it was only used for logging, and that logging statement is gone now.