lint: Don't set unused locals

Not a bug, but pointless to store this variable since it's not used.

.luacheckrc

@@ -5,7 +5,6 @@ return {
         "212", -- Unused argument.
         "212/self", -- Unused argument self.
         "213", -- Unused loop variable.
-        "231", -- Local variable is set but never accessed.
         "311", -- Value assigned to a local variable is unused.
         "631", -- Line is too long.
     },

stringx.lua

@@ -171,9 +171,7 @@ function stringx.deindent(s, keep_trailing_empty)
 	--split along newlines
 	local lines = stringx.split(s, newline)
 	--detect and strip any leading blank lines
-	local leading_newline = false
 	while lines[1] == "" do
-		leading_newline = true
 		table.remove(lines, 1)
 	end