drm/nouveau: Remove support for legacy contexts/buffers

drm/nouveau: Remove support for legacy contexts/buffers

Remove nouveau's support for legacy contexts and buffers. It was
required by libdrm earlier than 2.4.33, released in March 2012. A
previous attempt in 2013 to remove the functionality [1] had to be
reverted [2] as there were still users left. Libdrm 2.4.33 is now
almost 11 years old and it is time for userspace to move on.

With the nouveau code gone, we can also remove the driver-feature
bit DRIVER_KMS_LEGACY_CONTEXT.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c510133d93dd6f15ca040733ba7b2891ed61fd1
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c21eb21cb50d58e7cbdcb8b9e7ff68b85cfa5095
Link: https://patchwork.freedesktop.org/patch/msgid/20230112133858.17087-1-tzimmermann@suse.de