Removed duplicate definitions.

Duplicate definitions in csp.h caused compile errors with avr-gcc version < 4.6[1].

Specifically, the compile error was (when using makefile from subsystems directory):
```
In file included from ../../../../libcsp/src/arch/freertos/csp_queue.c:28:0:
../lib/libcsp/include/csp/csp.h:222:3: error: redefinition of typedef ‘csp_iface_t’
../lib/libcsp/include/csp/csp.h:200:28: note: previous declaration of ‘csp_iface_t’ was here
../lib/libcsp/include/csp/csp.h:226:15: error: redefinition of typedef ‘nexthop_t’
../lib/libcsp/include/csp/csp.h:201:15: note: previous declaration of ‘nexthop_t’ was here
```
[1] typedef redefinition is a part of C11 and implemented in avr-gcc 4.6: http://gcc.gnu.org/gcc-4.6/changes.html#c