[docs] Tweak parameter names for fcntl module (issue 22832)

[storchaka at gmail.com]

https://bugs.python.org/review/22832/diff/14277/Doc/library/fcntl.rst
File Doc/library/fcntl.rst (right):

https://bugs.python.org/review/22832/diff/14277/Doc/library/fcntl.rst#newcode31
Doc/library/fcntl.rst:31: .. function:: fcntl(fd, cmd[, arg=0])
Brackets are not needed longer.

https://bugs.python.org/review/22832/diff/14277/Doc/library/fcntl.rst#newcode53
Doc/library/fcntl.rst:53: .. function:: ioctl(fd, request[, arg=0[,
mutate_flag=True]])
And here too.

https://bugs.python.org/review/22832/diff/14277/Doc/library/fcntl.rst#newcode108
Doc/library/fcntl.rst:108: .. function:: lockf(fd, cmd, [len=0,
[start=0, [whence=0]]])
And here too.

https://bugs.python.org/review/22832/