test(e2e): remove unused capbset probe

The probe was added with the original rootless Podman CI lane in #2119 while investigating #2075. The reported failure was later traced to mismatched gateway and sandbox versions rather than rootless Podman capability-set handling.

Since #2981 removed the direct rootless Podman job, this probe no longer has a caller and does not represent active coverage.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

Author: elezar