RemoteLinux: Move environment handling entirely into the aspect class.

There is no reason why the run configuration should add its own logic on
top of what the aspect class does.
This makes RemoteLinuxRunConfiguration::environment() purely a
convenience method.

Change-Id: I80c4ede9a35388e7d3727fff90531accd7fc08de
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>