Remove pywin32 dependency

[vidartf]

Its use was removed in #483, so we can drop it now.

[SylvainCorlay]

There is still a small comment about pywin32 here.

jupyter_client/jupyter_client/win_interrupt.py

Lines 16 to 23 in 44980c1

	"""
	# Create a security attributes struct that permits inheritance of the
	# handle by new processes.
	# FIXME: We can clean up this mess by requiring pywin32 for IPython.
	class SECURITY_ATTRIBUTES(ctypes.Structure):
	_fields_ = [ ("nLength", ctypes.c_int),
	("lpSecurityDescriptor", ctypes.c_void_p),
	("bInheritHandle", ctypes.c_int) ]

[vidartf]

@SylvainCorlay Yes, but that has been around since before the dependency was added in #483, and should remain as it is.

[vidartf]

Note: If/when this gets released, the conda-forge feedstock can be put back to noarch as well, cc @minrk

[meeseeksmachine]

This pull request has been mentioned on Jupyter Community Forum. There might be relevant details there:

https://discourse.jupyter.org/t/jupyter-client-6-0-0/3414/1