Remove software-properties-common from dev container after use (#7255)

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