REORG: include: move the BUG_ON() code to haproxy/bug.h

REORG: include: move the BUG_ON() code to haproxy/bug.h

This one used to be stored into debug.h but the debug tools got larger
and require a lot of other includes, which can't use BUG_ON() anymore
because of this. It does not make sense and instead this macro should
be placed into the lower includes and given its omnipresence, the best
solution is to create a new bug.h with the few surrounding macros needed
to trigger bugs and place assertions anywhere.

Another benefit is that it won't be required to add include <debug.h>
anymore to use BUG_ON, it will automatically be covered by api.h. No
less than 32 occurrences were dropped.

The FSM_PRINTF macro was dropped since not used at all anymore (probably
since 1.6 or so).