ci/piglit: Consolidate identical skip lists for X11 and gbm

The tests skipped in x11-skips.txt and gbm-skips.txt were identical,
so consolidate them into the common all-skips.txt file.

Signed-off-by: Valentine Burley <valentine.burley@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34424>

.gitlab-ci/all-skips.txt

@@ -90,3 +90,26 @@ dEQP-VK.api.version_check.unavailable_entry_points
 spec@arb_program_interface_query@arb_program_interface_query-getprogramresourceindex
 spec@arb_program_interface_query@arb_program_interface_query-getprogramresourceindex@'vs_input2[1][0]' on GL_PROGRAM_INPUT
 
+# These tests attempt to read from the front buffer after a swap. They are skipped
+# on both X11 and gbm, but for different reasons:
+#
+# On X11: Given that we run piglit tests in parallel in Mesa CI, and don't have a
+# compositor running, the frontbuffer reads may end up with undefined results from
+# windows overlapping us.
+# Piglit does mark these tests as not to be run in parallel, but deqp-runner
+# doesn't respect that.  We need to extend deqp-runner to allow some tests to be
+# marked as single-threaded and run after the rayon loop if we want to support
+# them.
+# Other front-buffer access tests like fbo-sys-blit, fbo-sys-sub-blit, or
+# fcc-front-buffer-distraction don't appear here, because the DRI3 fake-front
+# handling should be holding the pixels drawn by the test even if we happen to fail
+# GL's window system pixel occlusion test.
+# Note that glx skips don't appear here, they're in all-skips.txt (in case someone
+# sets PIGLIT_PLATFORM=gbm to mostly use gbm, but still has an X server running).
+#
+# On gbm: gbm does not support reading the front buffer after a swapbuffers, and
+# that's intentional. Don't bother running these tests when PIGLIT_PLATFORM=gbm.
+# Note that this doesn't include tests like fbo-sys-blit, which draw/read front
+# but don't swap.
+spec@!opengl 1.0@gl-1.0-swapbuffers-behavior
+spec@!opengl 1.1@read-front

.gitlab-ci/deqp-runner.sh

@@ -69,14 +69,6 @@ if [ -e "$INSTALL/$GPU_VERSION-slow-skips.txt" ] && [[ $CI_JOB_NAME != *full* ]]
     DEQP_SKIPS="$DEQP_SKIPS $INSTALL/$GPU_VERSION-slow-skips.txt"
 fi
 
-if [ "$PIGLIT_PLATFORM" != "gbm" ] ; then
-    DEQP_SKIPS="$DEQP_SKIPS $INSTALL/x11-skips.txt"
-fi
-
-if [ "$PIGLIT_PLATFORM" = "gbm" ]; then
-    DEQP_SKIPS="$DEQP_SKIPS $INSTALL/gbm-skips.txt"
-fi
-
 if [ -n "$ANGLE_TAG" ]; then
     DEQP_SKIPS="$DEQP_SKIPS $INSTALL/angle-skips.txt"
 fi

.gitlab-ci/gbm-skips.txt

@@ -1,7 +0,0 @@
-# gbm does not support reading the front buffer after a swapbuffers, and that's
-# intentional. Don't bother running these tests when PIGLIT_PLATFORM=gbm.
-#
-# Note that this doesn't include tests like fbo-sys-blit, which draw/read front
-# but don't swap.
-spec@!opengl 1.0@gl-1.0-swapbuffers-behavior
-spec@!opengl 1.1@read-front

.gitlab-ci/x11-skips.txt

@@ -1,19 +0,0 @@
-# These tests all read from the front buffer after a swap.  Given that we
-# run piglit tests in parallel in Mesa CI, and don't have a compositor
-# running, the frontbuffer reads may end up with undefined results from
-# windows overlapping us.
-#
-# Piglit does mark these tests as not to be run in parallel, but deqp-runner
-# doesn't respect that.  We need to extend deqp-runner to allow some tests to be
-# marked as single-threaded and run after the rayon loop if we want to support
-# them.
-#
-# Other front-buffer access tests like fbo-sys-blit, fbo-sys-sub-blit, or
-# fcc-front-buffer-distraction don't appear here, because the DRI3 fake-front
-# handling should be holding the pixels drawn by the test even if we happen to fail
-# GL's window system pixel occlusion test.
-#
-# Note that glx skips don't appear here, they're in all-skips.txt (in case someone
-# sets PIGLIT_PLATFORM=gbm to mostly use gbm, but still has an X server running).
-spec@!opengl 1.0@gl-1.0-swapbuffers-behavior
-spec@!opengl 1.1@read-front