Skyrim: Remove CONFIG_SYSTEM_UNLOCKED
Skyrim is at a stage where this CONFIG can be removed.
BRANCH=None
TEST=zmake build skyrim; boot up on a D4 skyrim
# Skyrim reference-board-specific Kconfig settings.
CONFIG_BOARD_SKYRIM=y
-# TODO(b/215404321): Remove later in board development
+# CBI WP pin present
CONFIG_PLATFORM_EC_EEPROM_CBI_WP=y
-CONFIG_PLATFORM_EC_SYSTEM_UNLOCKED=y
# LED
CONFIG_PLATFORM_EC_LED_DT=y
