nanobsd: Provide empty routines for new embedded scheme

calculate_partitioning and create_code_slice are now required in
nanobsd.sh. While things work with the ones provided by legacy.sh, it's
fighting embedded/common's other actions. Instead, replace them with
stubs.

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tools/tools/nanobsd/embedded/common

@@ -647,6 +647,14 @@ esac
 
 NANO_SLICE_DATA=		# Not included
 
+# These don't make any sense to this strategy, so stub them out.
+calculate_partitioning ( ) (
+)
+
+# These don't make any sense to this strategy, so stub them out.
+create_code_slice ( ) (
+)
+
 # Each major disk scheme has its own routine. Generally
 # this is for mbr, gpt, etc. These are generally are widely
 # shared, but some specialized formats won't be shared.