Print pthread stub messages to Genode log console

With this patch, the 'not implemented' messages of the pthread function
stubs always get printed to the Genode log console instead of stdout.

Issue #815.
bash: don't call 'check_dev_tty()'

The 'check_dev_tty()' function calls 'ttyname()', which calls the pthread
stub function 'pthread_main_np()', which prints a 'not implemented'
message. Calling 'check_dev_tty()' doesn't seem to be necessary, so this
patch removes the call.

Issue #815.