Use a different saner syntax for pcall

takes less lines, looks much better

remove neoscroll.lua, missed in 2952f4d5c7

lua/plugins/nvimtree.lua

@@ -1,14 +1,9 @@
-local tree_cb
-if
-    not pcall(
-        function()
-            tree_cb = require "nvim-tree.config".nvim_tree_callback
-        end
-    )
- then
+local present, tree_c = pcall(require, "nvim-tree.config")
+if not present then
     return
 end
 
+local tree_cb = tree_c.nvim_tree_callback
 local g = vim.g
 
 vim.o.termguicolors = true