Remove the remnants of the legacy trace functionality (since replaced with FreeRTOS+Trace).

Replaced the #error that traps configMAX_SYSCALL_INTERRUPT_PRIORITY being set to 0 with a configASSERT() for GCC Cortex-M3/4 ports as the #error does not work if configMAX_SYSCALL_INTERRUPT_PRIORITY includes any casting.  Not a problem for other compilers as they cannot have casting anyway as that would break the assembly code.

FreeRTOS/Source/portable/IAR/ATMega323/port.c

@@ -280,7 +280,6 @@ portBASE_TYPE xPortStartScheduler( void )
 	compiler does not fully support inline assembler we have to make a call.*/
 	vPortStart();
 
-
 	/* Should not get here! */
 	return pdTRUE;
 }