ci/Dockerfile: Do not build r600

This will speed-up the compilation time.

Signed-off-by: Elie Tournier <elie.tournier@collabora.com>
Reviewed-By: Gert Wollny <gert.wollny@collabora.com>

ci/Dockerfile

@@ -169,7 +169,7 @@ RUN git clone --shallow-since="$GIT_DATE" https://gitlab.freedesktop.org/mesa/me
     git log --oneline -n 1 && \
     mkdir -p build && \
     meson build/ && \
-    meson configure build/ -Dprefix=/usr/local -Dplatforms=drm,x11,wayland,surfaceless -Ddri-drivers=i965 -Dgallium-drivers=swrast,virgl,radeonsi,r600 -Dbuildtype=debugoptimized -Dllvm=true -Dglx=dri -Dgallium-vdpau=false -Dgallium-va=false -Dvulkan-drivers=[] -Dlibdir=lib && \
+    meson configure build/ -Dprefix=/usr/local -Dplatforms=drm,x11,wayland,surfaceless -Ddri-drivers=i965 -Dgallium-drivers=swrast,virgl,radeonsi -Dbuildtype=debugoptimized -Dllvm=true -Dglx=dri -Dgallium-vdpau=false -Dgallium-va=false -Dvulkan-drivers=[] -Dlibdir=lib && \
     ninja -C build/ install && \
     rm -rf /mesa
 WORKDIR /