drm/ttm: remove ttm_bo_validate_swapout test

drm/ttm: remove ttm_bo_validate_swapout test

The test is quite fragile since it tries to allocate halve available system
memory + 1 page.

If the system has either not enough memory to make the allocation work
with other things running in parallel or to much memory so the allocation
fails as to large/invalid the test will fail.

Completely remove the test. We already validate swapout on the device
level and that test seems to be stable.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250710144129.1803-2-christian.koenig@amd.com