Since the meson build system rework, the configure script prefers the
git submodules over the system libraries. So we are testing compilation
with capstone, fdt and libslirp as a submodule all over the place,
burning CPU cycles by recompiling these third party modules and wasting
some network bandwidth in the CI by cloning the submodules each time.
Let's stop doing that in at least a couple of jobs and use the system
libraries instead.

While we're at it, also install meson in the Fedora container, since
it is new enough already, so we do not need to check out the meson
submodule here.

Message-Id: <20210121174451.658924-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>