setup: don't install ccache

I don't think the PX4 setup script should decide whether a user is to
use ccache or not. Anecdotally, I've heard from some in the dev team
that they are not using it themselves, so I don't think there is a good
basis to push it onto others.

That being said, we can of course still use ccache as part of the CI
builds nevertheless.

Tools/setup/arch.sh

@@ -48,7 +48,6 @@ echo "Installing PX4 general dependencies"
 sudo pacman -Sy --noconfirm --needed \
 	astyle \
 	base-devel \
-	ccache \
 	clang \
 	cmake \
 	cppcheck \