tipc: remove print_buf and deprecated log buffer code

The internal log buffer handling functions can now safely be
removed since there is no code using it anymore.  Requests to
interact with the internal tipc log buffer over netlink (in
config.c) will report 'obsolete command'.

This represents the final removal of any references to a
struct print_buf, and the removal of the struct itself.
We also get rid of a TIPC specific Kconfig in the process.

Finally, log.h is removed since it is not needed anymore.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>