Revert "kernel: banner: Expose tainted builds"

This reverts commit 6d4031f.

Those makes majority of builds og platforms with blobs tainted although
the blob were not used or compiled in. So it is very misleading.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

kernel/Kconfig

@@ -450,7 +450,6 @@ config BOOT_BANNER
 config BOOT_BANNER_STRING
 	string "Boot banner string"
 	depends on BOOT_BANNER
-	default "Booting Zephyr OS build (tainted)" if TAINT
 	default "Booting Zephyr OS build"
 	help
 	  Use this option to set the boot banner.