python: remove the default optimization

python: remove the default optimization

We had hard coded python-native and python's default optimization to 1,
which made the "assert" statement didn't work, and removed the "-O/-OO"
(optimization options), the target python had a "-N" option to disable
the default optimization, but the native python didn't.

I think that we can set the environment variable PYTHONOPTIMIZE or use
"python -O" if we need to optimize, but I'm not sure whether we need to
set it by default, it would confuse the user or cause/hide unexpected
problems if the "assert" doesn't work.

[YOCTO #4427]

(From OE-Core rev: 165ed464bbb9bf985dde9d8c15d000809901fff6)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>