test: Lua 5.2/5.3 compat

close #9515
ref #9280

test/functional/helpers.lua

@@ -1,4 +1,3 @@
-require('vim.compat')
 require('coxpcall')
 local luv = require('luv')
 local lfs = require('lfs')

test/helpers.lua

@@ -1,3 +1,4 @@
+require('vim.compat')
 local assert = require('luassert')
 local luv = require('luv')
 local lfs = require('lfs')

test/unit/api/helpers.lua

@@ -114,8 +114,7 @@ local lua2obj_type_tab = {
                      api.xmalloc(len * ffi.sizeof('KeyValuePair'))),
     }})
     for i = 1, len do
-      local table_unpack = table.unpack or unpack  -- luacheck: compat
-      local key, val = table_unpack(kvs[i])
+      local key, val = unpack(kvs[i])
       dct.data.dictionary.items[i - 1] = ffi.new(
           'KeyValuePair', {key=ffi.gc(lua2obj(key), nil).data.string,
                            value=ffi.gc(lua2obj(val), nil)})