unnecessary forced keys/query in triggerComputeTrust of MXRoomSummary

[BillCarsonFr]

MXRoomSummary will force download all keys of room members for no reason.
Triggerd on init, Can be trigger when member count change and some other triggers.

There is no real reason for MXRoomSummary to do that, it should compute trust without forcing key downloads.
The keys should already be downloaded:

• When a members join an encrypted, his keys will be tracked
• When loading members of a lazy loading the member's devices will be tracked
• when setting encryption.

Would be probably better to listen to MXDeviceListDidUpdateUsersDevicesNotification and then if one of the member is present in the change list to then compute trust (with force download = false)