[LOG] removed logging of exceptions in sendToSessionUser method

I looks a little bit strange to see something like

ERROR: could not send ...

immediately followed by 

WARN: sending failed ...

Let the caller handling the correct logging of the exception.

Change-Id: I2b2fca2900a1bb89ecf773f396163555fb7a0e37
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1147
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>