ostree: Replace libsoup_2_4 with libsoup_3
We are using curl backend since 58ed9b3b2a387f1bfcfc9c1525e0c4c76fcc33aa
but libsoup is still used for trivial-httpd for tests.
Let’s just switch to libsoup_3 so that we can drop 2.4.
Also since we no longer use libsoup, we do not need glib-networking or
even wrapping (introduced in a350ad306aa8ee0a9d4fc28c533cad4e4c5493f5
to make libsoup support HTTPS).