sw/petalinux/python: Remove run-time dependency of python3-pycparser on cpp and cpp-symlinks

python3-pytest depends on
python3-attrs->python3-cryptography->python3-pycparser
but features used in pytest do not need cpp nor cpp-symlinks.
This reduces the size of rootfs image by ~8MB

Signed-off-by: Adam Wujek <dev_public@wujek.eu>