Make some Stairs+ functions local and add Luacheck ignores

Those functions are used in various places in the mod,
so they aren't unused.

stairsplus/custom.lua

@@ -61,7 +61,8 @@ local subset = {
 }
 --]]
 
-function register_custom_subset(subset, modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_custom_subset(subset, modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_custom_subset(subset, modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,

stairsplus/init.lua

@@ -58,7 +58,8 @@ function stairsplus:register_alias_force_all(modname_old, subname_old, modname_n
 	self:register_micro_alias_force(modname_old, subname_old, modname_new, subname_new)
 end
 
-function register_stair_slab_panel_micro(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_stair_slab_panel_micro(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_all(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,

stairsplus/microblocks.lua

@@ -7,7 +7,8 @@ Licensed under the zlib license. See LICENSE.md for more information.
 
 -- Node will be called <modname>:micro_<subname>
 
-function register_micro(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_micro(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_micro(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,

stairsplus/panels.lua

@@ -7,7 +7,8 @@ Licensed under the zlib license. See LICENSE.md for more information.
 
 -- Node will be called <modname>:panel_<subname>
 
-function register_panel(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_panel(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_panel(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,

stairsplus/slabs.lua

@@ -5,11 +5,10 @@ Copyright © 2011-2019 Hugo Locurcio and contributors.
 Licensed under the zlib license. See LICENSE.md for more information.
 --]]
 
-local S = moreblocks.S
-
 -- Node will be called <modname>:slab_<subname>
 
-function register_slab(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_slab(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_slab(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,
@@ -36,7 +35,6 @@ end
 
 function stairsplus:register_slab(modname, subname, recipeitem, fields)
 	local defs = table.copy(stairsplus.defs["slab"])
-	local desc_base = S("%s Slab"):format(fields.description)
 	for alternate, shape in pairs(defs) do
 		stairsplus.register_single("slab", alternate, shape, modname, subname, recipeitem, fields)
 	end

stairsplus/slopes.lua

@@ -7,7 +7,8 @@ Licensed under the zlib license. See LICENSE.md for more information.
 
 -- Node will be called <modname>:slope_<subname>
 
-function register_slope(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_slope(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_slope(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,

stairsplus/stairs.lua

@@ -7,7 +7,8 @@ Licensed under the zlib license. See LICENSE.md for more information.
 
 -- Node will be called <modname>:stair_<subname>
 
-function register_stair(modname, subname, recipeitem, groups, images, description, drop, light)
+-- luacheck: no unused
+local function register_stair(modname, subname, recipeitem, groups, images, description, drop, light)
 	stairsplus:register_stair(modname, subname, recipeitem, {
 		groups = groups,
 		tiles = images,