ElementR: `client#scheduleAllGroupSessionsForBackup` should be deprecated or supported in rust

[BillCarsonFr]

https://github.com/matrix-org/matrix-js-sdk/blob/3c28cfc96ac6535b357b5e1d3b3180a0f00f87bb/src/client.ts#L3646

    public async scheduleAllGroupSessionsForBackup(): Promise<void> {
        if (!this.crypto) {
            throw new Error("End-to-end encryption disabled");
        }

        await this.crypto.backupManager.scheduleAllGroupSessionsForBackup();
    }

If called in rust crypto will wrongly fail with End-to-end encryption disabled

[BillCarsonFr]

Related #26919

[BillCarsonFr]

Don't need to do it in rust. Mark as deprecated and ignore on rust crypto

[richvdh]

scheduleAllGroupSessionsForBackup has been removed, so this is outdated