Revert "fix(models): disableRegistrationのデフォルト値が更新されていなかったので (MisskeyIO#442)" (MisskeyIO#444)

This reverts commit dea2e3183f.

packages/backend/src/models/Meta.ts

@@ -47,7 +47,7 @@ export class MiMeta {
 	public maintainerEmail: string | null;
 
 	@Column('boolean', {
-		default: true,
+		default: false,
 	})
 	public disableRegistration: boolean;