doc: develop: gsg: consolidate python3 install instructions for ubuntu

- Installing python3-venv should be done right when all dependencies are
  installed.
- Installing python3-venv is enough to pull wheel, setuptools
  (python3-setuptools-whl), and pip (python3-pip-whl) so that they are
  available in the venv, so reduce the list of packages to install
  accordingly.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

doc/develop/getting_started/index.rst

@@ -78,9 +78,8 @@ The current minimum required version for the main dependencies are:
          .. code-block:: bash
 
             sudo apt install --no-install-recommends git cmake ninja-build gperf \
-              ccache dfu-util device-tree-compiler wget \
+              ccache dfu-util device-tree-compiler wget python3-dev python3-venv python3-tk \
-              python3-dev python3-pip python3-setuptools python3-tk python3-wheel xz-utils file \
+              xz-utils file make gcc gcc-multilib g++-multilib libsdl2-dev libmagic1
-              make gcc gcc-multilib g++-multilib libsdl2-dev libmagic1
 
          .. note::
 
@@ -204,12 +203,6 @@ chosen. You'll also install Zephyr's additional Python dependencies in a
 
    .. group-tab:: Ubuntu
 
-      #. Use ``apt`` to install Python ``venv`` package:
-
-         .. code-block:: bash
-
-            sudo apt install python3-venv
-
       #. Create a new virtual environment:
 
          .. code-block:: bash