fix(pam): pass profile names to pam-auth-update --remove

[maybebyte]

Summary

The prerm/postrm scripts try to disable this package's PAM profiles when the
package is removed, but they pass the package name to pam-auth-update --remove,
which matches profile filenames — so the removal was silently a no-op. This
restores the intended early-disable and hardens the removal path across dpkg states.

Changes

• Root cause: pam-auth-update --remove matches the config filenames in
  /usr/share/pam-configs/ (readdir basenames), never the package name. Both
  scripts passed $DPKG_MAINTSCRIPT_PACKAGE (security-misc-shared), matching no
  profile, so nothing was removed. An unknown target is not validated and never
  errors, so it failed silently. The prerm early-disable was therefore dead:
  on removal, /etc/pam.d/common-* kept referencing helper scripts under
  /usr/libexec/security-misc/ that dpkg then deleted — and block-unsafe-logins
  is a Priority 1100 requisite, so a dangling reference fails all logins.
• prerm: pass the 8 actual profile filenames to --remove, guarded by
  command -v pam-auth-update. This is the man-page-documented purpose of
  --remove: strip profiles before the modules they reference leave disk.
• postrm: replace the inert --remove <pkg> with a plain
  pam-auth-update --package reconciliation scoped to remove|purge|disappear,
  so upgrade/abort-* never strip live hardening mid-transaction.

Testing

• Built a real security-misc-shared .deb (the actual profiles, the referenced
  helper scripts, and these maintainer scripts) and ran install → dpkg -r →
  dpkg -P in debian:stable-slim — 11/11 checks passed. Crux: same tree,
  only the --remove argument differs — --remove security-misc-shared left the
  profile in common-auth (old no-op reproduced), while --remove <8 filenames>
  removed it with the files still on disk; dpkg -r/-P exited 0 with
  common-* cleaned before the helper was deleted.
• Guard behavior confirmed: postrm invoked pam-auth-update only for
  remove/purge/disappear (not upgrade/abort-upgrade/abort-install/
  failed-upgrade/deconfigure), and postrm purge exited 0 with
  pam-auth-update absent from PATH.
• bash -n passes on both scripts; shellcheck is clean on the changed blocks.

Notes for reviewers

• On a normal remove/purge the observable end state is unchanged today —
  reconciliation already drops the profiles once their files are gone. This fix
  restores the prerm early-disable that closes the window where common-auth
  references a just-deleted module; it is a correctness/robustness fix, not a
  fix for a failure users currently hit.
• Decision: postrm keeps a plain --package (rather than dropping the call)
  as a safety net for profile-list drift and the disappear state, where prerm
  never runs. A real --remove <profiles> there was deliberately avoided — it
  would strip live hardening during upgrade/abort-*.
• Caveat: the 8-name list in prerm must stay in sync with
  debian/security-misc-shared.install and usr/share/pam-configs/; a forgotten
  profile is still reconciled away by the postrm net within the same dpkg run.