build.sh: Cleanup build requirements

Python 3.9 is already an old version which is still available on
prominent distros and thus an explicit installation need not be
a hard requirement. Also, `python3dist(flake8)` is not seen as
a system dependency during the build process other than the tox
environment for detecting linting errors.

Signed-off-by: Anoop C S <[email protected]>

Author: anoopcs9

tests/container/build.sh

@@ -121,10 +121,8 @@ task_sys_deps() {
         python3-wheel \
         python3-pyxattr \
         python3-devel \
-        python3.9 \
         samba-common-tools \
         rpm-build \
-        'python3dist(flake8)' \
         'python3dist(inotify-simple)' \
         'python3dist(mypy)' \
         'python3dist(pytest)' \