Blackfin: drop old u-boot.lds clean target

The u-boot.lds CPP unification missed the Blackfin-specific clean target.
It is no longer needed, so punt it.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>

Makefile

@@ -2436,7 +2436,6 @@ clean:
 	       $(obj)board/netstar/{eeprom,crcek,crcit,*.srec,*.bin}	  \
 	       $(obj)board/trab/trab_fkt   $(obj)board/voiceblue/eeprom   \
 	       $(obj)board/armltd/{integratorap,integratorcp}/u-boot.lds  \
-	       $(obj)arch/blackfin/lib/u-boot.lds				  \
 	       $(obj)u-boot.lds						  \
 	       $(obj)arch/blackfin/cpu/bootrom-asm-offsets.[chs]
 	@rm -f $(obj)include/bmp_logo.h