remove mariadb and mysql from _helpers.tpl (#421)

### Description of the change

Removes checks for mariadb and mysql from _helpers.tpl

### Benefits

Fixes the helm-chart version 8.0.0 if using a external database

### Applicable issues

- fixes #420
- fixes #419

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/421
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Reviewed-by: John Olheiser <john+gitea@jolheiser.com>
Reviewed-by: delvh <dev.lh@web.de>
Reviewed-by: yardenshoham <yardenshoham@noreply.gitea.io>
Co-authored-by: Maximilian Marschall <maximilian.marschall@3xm.at>
Co-committed-by: Maximilian Marschall <maximilian.marschall@3xm.at>

templates/_helpers.tpl

@@ -287,22 +287,6 @@ https
     {{- $_ := set .Values.gitea.config.database "NAME"      .Values.postgresql.global.postgresql.auth.database -}}
     {{- $_ := set .Values.gitea.config.database "USER"      .Values.postgresql.global.postgresql.auth.username -}}
     {{- $_ := set .Values.gitea.config.database "PASSWD"    .Values.postgresql.global.postgresql.auth.password -}}
-  {{- else if .Values.mysql.enabled -}}
-    {{- $_ := set .Values.gitea.config.database "DB_TYPE"   "mysql" -}}
-    {{- if not (.Values.gitea.config.database.HOST) -}}
-      {{- $_ := set .Values.gitea.config.database "HOST"      (include "mysql.dns" .) -}}
-    {{- end -}}
-    {{- $_ := set .Values.gitea.config.database "NAME"      .Values.mysql.db.name -}}
-    {{- $_ := set .Values.gitea.config.database "USER"      .Values.mysql.db.user -}}
-    {{- $_ := set .Values.gitea.config.database "PASSWD"    .Values.mysql.db.password -}}
-  {{- else if .Values.mariadb.enabled -}}
-    {{- $_ := set .Values.gitea.config.database "DB_TYPE"   "mysql" -}}
-    {{- if not (.Values.gitea.config.database.HOST) -}}
-      {{- $_ := set .Values.gitea.config.database "HOST"      (include "mariadb.dns" .) -}}
-    {{- end -}}
-    {{- $_ := set .Values.gitea.config.database "NAME"      .Values.mariadb.auth.database -}}
-    {{- $_ := set .Values.gitea.config.database "USER"      .Values.mariadb.auth.username -}}
-    {{- $_ := set .Values.gitea.config.database "PASSWD"    .Values.mariadb.auth.password -}}
   {{- end -}}
 {{- end -}}