Remove mysql and mariadb chart deps (#417)

As discussed in Discord.

Supersedes #412 and #407.

**⚠️ BREAKING**

Users depending on the built-in MySQL or MariaDB chart have to switch to an self-managed database, or Postgres

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/417
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Reviewed-by: John Olheiser <john+gitea@jolheiser.com>
Reviewed-by: yardenshoham <yardenshoham@noreply.gitea.io>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

Chart.lock

@@ -2,14 +2,8 @@ dependencies:
 - name: memcached
   repository: oci://registry-1.docker.io/bitnamicharts
   version: 6.3.7
-- name: mysql
-  repository: https://raw.githubusercontent.com/bitnami/charts/pre-2022/bitnami
-  version: 6.14.10
 - name: postgresql
   repository: oci://registry-1.docker.io/bitnamicharts
   version: 12.2.6
-- name: mariadb
-  repository: https://raw.githubusercontent.com/bitnami/charts/pre-2022/bitnami
-  version: 9.3.6
-digest: sha256:2115873999bfccaaa3308dd4cd374def696572938cc240079ea338b9d8fd9723
-generated: "2023-03-27T10:04:33.619453+02:00"
+digest: sha256:c2026881f71eca24c72e9da3e798a1ad2a5af8e86a39a5341015584eaacf8b64
+generated: "2023-03-27T19:20:21.125036+02:00"