I don't know if it is possible to suppress it. I think the call to the executable calls the packed perl script as a new process, so there are two related processes.

It is also independent of Tk. This packed one liner also has four associated processes on my Windows 10 machine, 2 x a.exe, 1 x Console Window Host and 1 x Windows Command Processor:

pp -e "while (1) {$n = 1}"
a.exe
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