Remove unnecessary sos_write just for stdout and link tty to libsosapi

[lucypa]

Writing to stdout/err and writing to files should not be treated differently in the API. This PR removes the special treatment just for tty_test and instead uses sos_sys_write. This also solves this jira issue. If merged, I will update the milestone 0 spec to reflect these changes. Implementation by students should remain the same but now students will write their first syscall in the libsosapi instead.

[lucypa]

Apologies some of the clean up commits made it in without me realising.