[MIPS] remove CONFIG_CPU_R4000 line from Makefile

The existing options are named CONFIG_CPU_R4300 and CONFIG_CPU_R4X00,
and they are directly below.
Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/Makefile

@@ -30,7 +30,6 @@ obj-$(CONFIG_CPU_LOONGSON2)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS32)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS64)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_R3000)		+= r2300_fpu.o r2300_switch.o
-obj-$(CONFIG_CPU_R4000)		+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_R4300)		+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_R4X00)		+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_R5000)		+= r4k_fpu.o r4k_switch.o