Remove useless tasks from matrix-postgres-backup role

`matrix-postgres-backup` reuses the `matrix-postgres` role for these
tasks, not its own definitions.

roles/matrix-postgres-backup/tasks/util/detect_existing_postgres_version.yml

@@ -1,61 +0,0 @@
----
-
-# This utility aims to determine if there is some existing Postgres version in use or not.
-# If there is, it also tries to detect the Docker image that corresponds to that version.
-
-- name: Initialize Postgres version determination variables (default to empty)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detection_pg_version_path: "{{ matrix_postgres_data_path }}/PG_VERSION"
-    matrix_postgres_backup_detected_existing: false
-    matrix_postgres_backup_detected_version: ""
-    matrix_postgres_backup_detected_version_corresponding_docker_image: ""
-
-- name: Determine existing Postgres version (check PG_VERSION file)
-  ansible.builtin.stat:
-    path: "{{ matrix_postgres_backup_detection_pg_version_path }}"
-  register: result_pg_version_stat
-
-- ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_existing: true
-  when: "result_pg_version_stat.stat.exists"
-
-- name: Determine existing Postgres version (read PG_VERSION file)
-  ansible.builtin.slurp:
-    src: "{{ matrix_postgres_backup_detection_pg_version_path }}"
-  register: result_pg_version
-  when: matrix_postgres_backup_detected_existing | bool
-
-- name: Determine existing Postgres version (make sense of PG_VERSION file)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version: "{{ result_pg_version['content'] | b64decode | replace('\n', '') }}"
-  when: matrix_postgres_backup_detected_existing | bool
-
-- name: Determine corresponding Docker image to detected version (assume default of latest)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_latest }}"
-  when: "matrix_postgres_backup_detected_version != ''"
-
-- name: Determine corresponding Docker image to detected version (use 9.x, if detected)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v9 }}"
-  when: "matrix_postgres_backup_detected_version.startswith('9.')"
-
-- name: Determine corresponding Docker image to detected version (use 10.x, if detected)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v10 }}"
-  when: "matrix_postgres_backup_detected_version == '10' or matrix_postgres_backup_detected_version.startswith('10.')"
-
-- name: Determine corresponding Docker image to detected version (use 11.x, if detected)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v11 }}"
-  when: "matrix_postgres_backup_detected_version == '11' or matrix_postgres_backup_detected_version.startswith('11.')"
-
-- name: Determine corresponding Docker image to detected version (use 12.x, if detected)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v12 }}"
-  when: "matrix_postgres_backup_detected_version == '12' or matrix_postgres_backup_detected_version.startswith('12.')"
-
-- name: Determine corresponding Docker image to detected version (use 13.x, if detected)
-  ansible.builtin.set_fact:
-    matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v13 }}"
-  when: "matrix_postgres_backup_detected_version == '13' or matrix_postgres_backup_detected_version.startswith('13.')"