make help: remove <pkg>-legal-info

The <pkg>-legal-info target is only a component of the top-level
legal-info target, it is not meant to be used alone.

For example, calling twice 'make busybox-legal-info' produces duplicate
entries in licenses.txt and manifest.csv.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Arnout Vandecappelle <arnout@mind.be>
Reviewed-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -876,7 +876,6 @@ help:
 	@echo '  <pkg>-dirclean         - Remove <pkg> build directory'
 	@echo '  <pkg>-reconfigure      - Restart the build from the configure step'
 	@echo '  <pkg>-rebuild          - Restart the build from the build step'
-	@echo '  <pkg>-legal-info       - Generate license information for <pkg>'
 ifeq ($(BR2_PACKAGE_BUSYBOX),y)
 	@echo '  busybox-menuconfig     - Run BusyBox menuconfig'
 endif