ci/deqp: drop the implicit DEQP_TARGET; explicitly set default in VK builds

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27250>

.gitlab-ci/container/build-deqp.sh

@@ -130,12 +130,12 @@ if [ "${DEQP_TARGET}" != 'android' ]; then
 fi
 
 cmake -S /VK-GL-CTS -B . -G Ninja \
-      -DDEQP_TARGET=${DEQP_TARGET:-default} \
+      -DDEQP_TARGET=${DEQP_TARGET} \
       -DCMAKE_BUILD_TYPE=Release \
       $EXTRA_CMAKE_ARGS
 
 # Make sure `default` doesn't silently stop detecting one of the platforms we care about
-if [ "${DEQP_TARGET:-default}" = 'default' ]; then
+if [ "${DEQP_TARGET}" = 'default' ]; then
   grep -q DEQP_SUPPORT_WAYLAND=1 build.ninja
   grep -q DEQP_SUPPORT_X11=1 build.ninja
   grep -q DEQP_SUPPORT_XCB=1 build.ninja

.gitlab-ci/container/debian/x86_64_test-vk.sh

@@ -104,6 +104,7 @@ PIGLIT_BUILD_TARGETS="piglit_replayer" . .gitlab-ci/container/build-piglit.sh
 ############### Build dEQP VK
 
 DEQP_API=VK \
+DEQP_TARGET=default \
 . .gitlab-ci/container/build-deqp.sh
 
 ############### Build apitrace

.gitlab-ci/container/lava_build.sh

@@ -277,6 +277,7 @@ DEQP_TARGET=surfaceless \
 . .gitlab-ci/container/build-deqp.sh
 
 DEQP_API=VK \
+DEQP_TARGET=default \
 . .gitlab-ci/container/build-deqp.sh
 
 mv /deqp $ROOTFS/.