ieee1394: drop csr1212's support for external compilation

csr1212 was written to be compiled either as part of the ieee1394 kernel
driver or of an anticipated IEEE 1212 userspace library.  We now drop
support for the latter.  The costs in terms of code footprint and depth
of abstraction are not countered by any actual benefit.

Also remove some obsolete #includes.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>