Remove software-properties-common from container after use

During the creation of the devcontainer we need to add a ppa
repository, which is easiest done via software-properies-common.
As turns out this installes pkexec into the container as a side
effect.

When vscode tries to attach a debugger it first checks if
pkexec is installed as this gives a nicer popup asking for
elevation of rights to attach to the process. However, since dev
containers don't have a windowing system running pkexec isn't
working as expected and thus prevents the debugger from attaching.

Without pkexec in the container vscode 'falls back' to plain old sudo
which we can run passwordless in the container.

For pkexec to be removed we need to first purge software-propertied-common
as well as autoremove all packages that were installed due to the
installation of said package. By performing this all in one step we
minimize the size of the layer we are creating.

.devcontainer/Dockerfile

@@ -36,6 +36,10 @@ RUN apt update && apt install -y \
  && add-apt-repository ppa:deadsnakes/ppa -y \
  && apt install -y \
     python3.9-full \
+ # software properties pulls in pkexec, which makes the debugger unusable in vscode
+ && apt purge -y \
+    software-properties-common \
+ && apt autoremove -y \
  && apt clean
 
 RUN sudo pip3 install pipenv pipenv-shebang
@@ -109,7 +113,7 @@ WORKDIR /uncrustify/uncrustify-uncrustify-0.68.1/
 RUN mkdir build
 WORKDIR /uncrustify/uncrustify-uncrustify-0.68.1/build/
 RUN cmake ..
-RUN make -sj8
+RUN MAKEFLAGS="-j $(nproc)" make -s
 
 RUN make install DESTDIR=/uncrustify