MIPS: drop redundant start_barebox() declaration

The start_barebox() function is defined in the <common.h> header file.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/mips/boot/main_entry.c

@@ -25,7 +25,6 @@
 #include <asm/mipsregs.h>
 #include <asm/addrspace.h>
 
-extern void start_barebox(void);
 extern void handle_reserved(void);
 
 void main_entry(void);