[INTERNAL] removed chat transfer fallback

The fallback is disabled since Saros version 13.3.22 .
Looking at various log files even the IBB stream fail
and so the fallback via chat would also fail.

Removed the fallback as it does not offer any benefits but
only worsen things when it comes to detect broken connections.

Change-Id: I6c4a80c30e8bbd0236b635d1dc7605512b979df6
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/970
Tested-by: Jenkins CI
Reviewed-by: Patrick Schlott <pschlottk@gmail.com>
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>