Use moreblocks as an optional dependency.

extranodes/depends.txt

@@ -1,6 +1,5 @@
 default
-moreblocks
 technic_worldgen
 concrete
 intllib?
-
+moreblocks?

extranodes/init.lua

@@ -3,6 +3,8 @@
 -- Boilerplate to support localized strings if intllib mod is installed.
 local S = rawget(_G, "intllib") and intllib.Getter() or function(s) return s end
 
+if minetest.get_modpath("moreblocks") then
+
 	-- register stairsplus/circular_saw nodes
 	-- we skip blast resistant concrete and uranium intentionally
 	-- chrome seems to be too hard of a metal to be actually sawable
@@ -97,3 +99,5 @@ register_technic_stairs_alias("stairsplus", "concrete", "technic", "concrete")
 	register_technic_stairs_alias("stairsplus", "marble", "technic", "marble")
 	register_technic_stairs_alias("stairsplus", "granite", "technic", "granite")
 	register_technic_stairs_alias("stairsplus", "marble_bricks", "technic", "marble_bricks")
+
+end