wayland: Drop ptrace logic

kwin disables ptrace for a good reason - to prevent other processes from
attaching to kwin and snooping sensitive data or taking control of kwin.
But, that will also make things such as memory statistics unavailable to
read, etc.

On the other hand, the supported platforms where kwin runs all have
security measures in places to forbid shady processes ptrace'ing kwin.
For example, on Linux it's YAMA.

On Linux, by default, a process can ptrace only its descendants. For
example, this can be used by debuggers; otherwise you would need to be
the superuser to attach to any process.

This change drops our ptrace logic in favor of system provided security
measures. It allows the System Monitor to gather kwin's memory usage
statistics and also simplifies code, the current debugger detection
logic is not really robust.

If the system provided security measures are proven to be insufficient,
we can add the ptrace disabling logic back, but it would be great to
avoid that because system monitor won't be able to gather resource usage
statistics, which can be useful for detecting memory leaks in plasma
wayland session, etc.