samples: cellular: modem_shell: Disable date shell on Thingy:91

Save flash in the constrained NS slot by turning off the Zephyr date
shell command on thingy91/nrf9160/ns.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

Author: rlubos

samples/cellular/modem_shell/boards/thingy91_nrf9160_ns.conf

@@ -22,6 +22,7 @@ CONFIG_SHELL_STATS=n
 CONFIG_DEVICE_SHELL=n
 CONFIG_DEVMEM_SHELL=n
 CONFIG_MCUBOOT_SHELL=n
+CONFIG_DATE_SHELL=n
 
 # MCUBOOT
 CONFIG_BOOTLOADER_MCUBOOT=y