chore(Layer): remove unused function

lua/libmodal/src/Layer.lua

@@ -11,16 +11,6 @@ local function normalize_buffer(buffer)
 	return buffer
 end
 
---- remove and return the right-hand side of a `keymap`.
---- @param keymap table the keymap to unpack
---- @return string lhs, table options
-local function unpack_keymap_lhs(keymap)
-	local lhs = keymap.lhs
-	keymap.lhs = nil
-
-	return lhs, keymap
-end
-
 --- remove and return the right-hand side of a `keymap`.
 --- @param keymap table the keymap to unpack
 --- @return function|string rhs, table options