drm/xe: Remove duplicate DRM_EXEC selection from Kconfig

There are 2 identical "select DRM_EXEC" lines for DRM_XE.
Remove one to clean up the configuration.

Fixes: d490ecf57790 ("drm/xe: Rework xe_exec and the VM rebind worker to use the drm_exec helper")
Cc: Thomas Hellström <[e-mail]>
Cc: Lucas De Marchi <[e-mail]>
Signed-off-by: Shuicheng Lin <[e-mail]>
Reviewed-by: Nitin Gote <[e-mail]>
Reviewed-by: Lucas De Marchi <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>
(cherry picked from commit b1aa02acd03bfef3ed39c511d33c4a4303d2f9b1)
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/Kconfig

···
 	select TMPFS
 	select DRM_BUDDY
 	select DRM_CLIENT_SELECTION
-	select DRM_EXEC
 	select DRM_KMS_HELPER
 	select DRM_KUNIT_TEST_HELPERS if DRM_XE_KUNIT_TEST != n
 	select DRM_PANEL