Don't register trigger on Python for securedrop-app-code package

We currently register a trigger with the Python
interpreter so dh_virtualenv can fix up the interpreter's symlinks
in case something changes as recommended in their docs[1].

However, our packages are designed for a single Ubuntu release, which
keeps the same version of Python for its entire lifetime, so the
interpreter in the venv will always be a symlink to `/usr/bin/python3`
and the dh_virtualenv postinst code will always be a no-op because it
skips all symlinks.

This was noticed because our custom postinst was not handling the
"triggered" state, which is valid per deb-postinst(5). Add that in for
future proofing even though we don't expect it to be called.

[1]
https://dh-virtualenv.readthedocs.io/en/latest/tutorial.html?highlight=trigger#step-2-set-up-packaging-for-your-project

Fixes #6230.

install_files/ansible-base/roles/build-securedrop-app-code-deb-pkg/defaults/main.yml

@@ -46,7 +46,3 @@ securedrop_venv: "/opt/venvs/securedrop-app-code"
 securedrop_venv_bin: "{{ securedrop_venv }}/bin"
 securedrop_python_version: "{{ '3.8' if securedrop_target_distribution == 'focal' else '3.5' }}"
 securedrop_venv_site_packages: "{{ securedrop_venv }}/lib/python{{ securedrop_python_version }}/site-packages"
-
-securedrop_app_focal_files:
-  - src: securedrop-app-code.triggers-focal
-    dest: "{{ securedrop_app_code_prep_dir }}/debian/securedrop-app-code.triggers"

install_files/ansible-base/roles/build-securedrop-app-code-deb-pkg/tasks/main.yml

@@ -60,13 +60,6 @@
     src: "changelog-{{ securedrop_target_distribution }}"
     dest: "{{ securedrop_app_code_prep_dir }}/debian/changelog"
 
-- name: Replace the files required for focal package
-  copy:
-    src: "{{ item.src }}"
-    dest: "{{ item.dest }}"
-  with_items: "{{ securedrop_app_focal_files }}"
-  when: securedrop_target_distribution == "focal"
-
 - name: Create the control file based on distribution
   template:
     src: "control.j2"

install_files/securedrop-app-code/debian/postinst

@@ -243,7 +243,7 @@ case "$1" in
 
     ;;
 
-    abort-upgrade|abort-remove|abort-deconfigure)
+    abort-upgrade|abort-remove|abort-deconfigure|triggered)
     ;;
 
     *)