java: Simplify uncaught exception reporting

As pointed out by Tomek, the call to printStackTrace() will already
print out the exception message.

Drop the "uncaught exception" messages to simplify things.

Acked-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>