Warning when mousekeys are disabled

[tmk]

Disabling mouse key in Makefile

#MOUSEKEY_ENABLE = yes

spits this warning.

mkdir -p obj_ps2_usb_lufa/common
Compiling C: ../../tmk_core/common/command.c
avr-gcc -c -mmcu=atmega32u4 -gdwarf-2 -DF_CPU=16000000UL -DBOOTLOADER_SIZE=512 -DPS2_USE_INT -DF_USB=16000000UL -DARCH=ARCH_AVR8 -DUSB_DEVICE_ONLY -DUSE_FLASH_DESCRIPTORS -DUSE_STATIC_OPTIONS="(USB_DEVICE_OPT_FULLSPEED | USB_OPT_REG_ENABLED | USB_OPT_AUTO_PLL)" -DFIXED_CONTROL_ENDPOINT_SIZE=8  -DFIXED_NUM_CONFIGURATIONS=1 -DPROTOCOL_LUFA -DEXTRAKEY_ENABLE -DCONSOLE_ENABLE -DCOMMAND_ENABLE -DNKRO_ENABLE -DVERSION=orphans-3-g3c10920-dirty -Os -funsigned-char -funsigned-bitfields -ffunction-sections -fdata-sections -fno-inline-small-functions -fpack-struct -fshort-enums -fno-strict-aliasing -Wall -Wstrict-prototypes -Wa,-adhlns=obj_ps2_usb_lufa/common/command.lst -I. -I../../tmk_core -I../../tmk_core/protocol -I../../tmk_core/protocol/lufa -I../../tmk_core/protocol/lufa/LUFA-git -I../../tmk_core/common -std=gnu99 -include config.h -MMD -MP -MF .dep/obj_ps2_usb_lufa_common_command.o.d  ../../tmk_core/common/command.c -o obj_ps2_usb_lufa/common/command.o 
../../tmk_core/common/command.c:624:16: warning: ‘numkey2num’ defined but not used [-Wunused-function]
 static uint8_t numkey2num(uint8_t code)