boards: cc2650_sensortag: Remove Kconfig FLASH/SRAM address assignments

The {FLASH,SRAM}_BASE_ADDRESS Kconfig symbols were removed in commit
311e6b9e ("arch: arc: Use DTS for all ARC SoCs"). These settings are
supposed to come from DTS now.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>