selftests/bpf: Remove test_access_variable_array

selftests/bpf: Remove test_access_variable_array

test_access_variable_array relied on accessing struct sched_domain::span
to validate variable-length array handling via BTF. Recent scheduler
refactoring removed or hid this field, causing the test
to fail to build.

Given that this test depends on internal scheduler structures that are
subject to refactoring, and equivalent variable-length array coverage
already exists via bpf_testmod-based tests, remove
test_access_variable_array entirely.

Link: https://lore.kernel.org/all/177434340048.1647592.8586759362906719839.tip-bot2@tip-bot2/
Signed-off-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Tested-by: Naveen Kumar Thummalapenta <naveen66@linux.ibm.com>
Link: https://lore.kernel.org/r/20260410105404.91126-1-venkat88@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>