ARC: configs: remove no longer needed CONFIG_DEVPTS_MULTIPLE_INSTANCES

Since commit eedf265a ("devpts: Make each mount of devpts an
independent filesystem.") CONFIG_DEVPTS_MULTIPLE_INSTANCES isn't needed
in the defconfig anymore.
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/configs/tb10x_defconfig

@@ -56,7 +56,6 @@ CONFIG_STMMAC_ETH=y
 # CONFIG_INPUT is not set
 # CONFIG_SERIO is not set
 # CONFIG_VT is not set
-CONFIG_DEVPTS_MULTIPLE_INSTANCES=y
 # CONFIG_LEGACY_PTYS is not set
 # CONFIG_DEVKMEM is not set
 CONFIG_SERIAL_8250=y