lualoader: clear up some luacheck warnings

- One (1) unused argument
- One (1) trailing whitespace
- Two (2) "non-standard global" (curenv, rewind)

tools/boot/lua-lint.sh is once again happy.

stand/lua/cli.lua

@@ -130,7 +130,7 @@ cli['read-conf'] = function(...)
 	config.readConf(assert(core.popFrontTable(argv)))
 end
 
-cli['reload-conf'] = function(...)
+cli['reload-conf'] = function()
 	config.reload()
 end
 

stand/lua/core.lua

@@ -319,7 +319,7 @@ function core.bootenvDefaultRewinded()
 	end
 
 	for curenv_idx = 0, bootenv_count - 1 do
-		curenv = loader.getenv("bootenvs_check[" .. curenv_idx .. "]")
+		local curenv = loader.getenv("bootenvs_check[" .. curenv_idx .. "]")
 		if curenv == defname then
 			return defname
 		end

stand/lua/menu.lua

@@ -352,7 +352,7 @@ menu.welcome = {
 		zpool_checkpoints = {
 			entry_type = core.MENU_ENTRY,
 			name = function()
-				rewind = "No"
+				local rewind = "No"
 				if core.isRewinded() then
 					rewind = "Yes"
 				end