Match the fwup behavior change (commit to controller XSPI slot 0, no
pre-erase): remove the drive_ctrl_pre_erase helper and its call sites, assert
the UPDATE commit targets slot 0, rename the locked-mode-workaround test to
test_ctrl_update_commits_slot0 (caller's slot ignored -> slot 0), and remove
the obsolete test_ctrl_update_pre_erase_fails.  29/29 driver tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>