kconfig: Remove remnants of unimplemented BUILD_TIMESTAMP feature

The Kconfig option CONFIG_BUILD_TIMESTAMP became unused when
BUILD_VERSION was introduced, but it's option and parts of it's
implementation was not completely cleaned from the repository.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>

kernel/Kconfig

@@ -300,9 +300,7 @@ config BOOT_BANNER
 	select PRINTK
 	select EARLY_CONSOLE
 	help
-	  This option outputs a banner to the console device during boot up. It
-	  also embeds a date & time stamp in the kernel if the BUILD_TIMESTAMP
-	  option is enabled.
+	  This option outputs a banner to the console device during boot up.
 
 config BOOT_DELAY
 	int "Boot delay in milliseconds"
@@ -317,13 +315,6 @@ config BOOT_DELAY
 	  achieved by waiting for DCD on the serial port--however, not
 	  all serial ports have DCD.
 
-config BUILD_TIMESTAMP
-	bool "Build Timestamp"
-	help
-	  Record a timestamp from the build and add it to the boot banner.
-	  Note that this will make the build unreproducible: building
-	  Zephyr twice will result in different binaries.
-
 config INT_LATENCY_BENCHMARK
 	bool "Interrupt latency metrics [EXPERIMENTAL]"
 	depends on ARCH="x86"

kernel/init.c

@@ -34,9 +34,6 @@
 #include <tracing.h>
 #include <stdbool.h>
 
-/* kernel build timestamp items */
-#define BUILD_TIMESTAMP "BUILD: " __DATE__ " " __TIME__
-
 /* boot banner items */
 #if defined(CONFIG_BOOT_DELAY) && CONFIG_BOOT_DELAY > 0
 #define BOOT_DELAY_BANNER " (delayed boot "	\

samples/boards/nrf52/mesh/onoff-app/prj.conf

@@ -12,7 +12,6 @@ CONFIG_SETTINGS_FCB=y
 CONFIG_BT_MESH_RPL_STORE_TIMEOUT=600
 
 CONFIG_BOOT_BANNER=y
-CONFIG_BUILD_TIMESTAMP=y
 
 CONFIG_BT_OBSERVER=y
 CONFIG_BT_BROADCASTER=y

tests/drivers/spi/spi_loopback/prj_base.conf

@@ -1,6 +1,5 @@
 CONFIG_TEST=y
 CONFIG_BOOT_BANNER=y
-CONFIG_BUILD_TIMESTAMP=y
 CONFIG_SYS_LOG=y
 CONFIG_SPI=y
 CONFIG_SPI_ASYNC=y