Remove SyncFileItem::log

Remove SyncFileItem::log

This remove the remaining "other" fields of the sync log to save a
bit of memory.

other_etag and other_fileId don't give much information to the users
and other_instruction will always be INST_NONE anyway.

other_modtime and other_size are kept since they are sometimes used.
They were renamed to have a bit more meaningful name.

SyncEngine::checkPermissions will now fetch its information from the
csync trees since they are now preserved until right after this point.

Fixes #3213