boards: kconfig: Do not assign promptless SOC_FAMILY_TISIMPLELINK

Assignments have no effect on promptless symbols. Flagged by
https://github.com/zephyrproject-rtos/zephyr/pull/20742

.

This symbol is selected by the SOC_SERIES_CC13X2_CC26X2,
SOC_SERIES_CC2650, SOC_SERIES_CC32XX, and SOC_SERIES_MSP432P4XX symbols.

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