PYTHON_PN is on its way out, therefore it's good to remove it from
documentation so its use is not promoted anymore.
(From yocto-docs rev: 74180c0f6bcdeadbd6f9a69d26f733c716f420fd)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>