Remove empty __init__ methods

[sobolevn]

I've removed all def __init__(self) definitions if they are:

• Defined in a class that inherits directly from object, like TaskGroup
• Or defined in a class that inherits from other classes with no custom __init__ set, like PidfdChildWatcher
• Is not used as a part of @overload

They are not needed, because object already provides this method.
Keeping the stubs minimal is better for future maintenance.

There are some complex cases that I've left for now like stdlib/xml/dom/minidom.pyi, because it is not fully annotated yet.

Refs #8594

[sobolevn]

Stubtest fails with:

note: unused allowlist entry _csv.Dialect.__init__
note: unused allowlist entry queue.SimpleQueue.__init__
note: unused allowlist entry select.kqueue.__init__

Looking into it.

[sobolevn]

Ok, I removed from this PR all three cases that are listed in allowlists.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉