rdp-backend: require FreeRDP >= 2.2 to remove all the version hacks

The stable FreeRDP 2.x branch has been released, so let's rely on that maintained
version and drop all the hacks for older versions. That makes the code and build
cleaner.

Signed-off-by: David Fort <contact@hardening-consulting.com>

.gitlab-ci/debian-install.sh

@@ -36,7 +36,6 @@ apt-get -y --no-install-recommends install \
 	build-essential \
 	curl \
 	doxygen \
-	freerdp2-dev \
 	git \
 	libasound2-dev \
 	libbluetooth-dev \
@@ -92,6 +91,8 @@ apt-get -y --no-install-recommends install \
 	xwayland \
 	$MESA_RUNTIME_PKGS
 
+apt-get -y --no-install-recommends -t buster-backports install \
+	freerdp2-dev
 
 pip3 install --user git+https://github.com/mesonbuild/meson.git@0.49
 export PATH=$HOME/.local/bin:$PATH
@@ -161,4 +162,4 @@ cd ..
 rm -rf pipewire
 
 apt-get -y --autoremove purge $LINUX_DEV_PKGS
-apt-get -y --autoremove purge $MESA_DEV_PKGS
+apt-get -y --autoremove purge $MESA_DEV_PKGS