killav: Cleanup and support non-meterpreter sessions

[bcoles]

Note: requires #16900 to be merged first.

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Resolves Rubocop violations.

Adds documentation.

Adds Notes module meta information.

Adds support for non-Meterpreter sessions. Uses Msf::Post::Process.kill_process(pid). (#16900)

Removes an unnecessary incremental count variable.