Cleanup various varargs shenanigans (#9624)

* Iterate over varargs directly via select if possible
* Use table.pack otherwise (https://github.com/koreader/koreader-base/pull/1535).
* This allows us to simplify a few Logger calls, as logger now handles nil values.

frontend/util.lua

@@ -1535,12 +1535,6 @@ local WrappedFunction_mt = {
     end,
 }
 
---- Helper function to help dealing with nils in varargs, since we don't have table.pack w/o Lua 5.2 compat...
---- Unpack w/ unpack(t, 1, t.n)
-function util.table_pack(...)
-    return { n = select("#", ...), ... }
-end
-
 --- Wrap (or replace) a table method with a custom method, in a revertable way.
 -- This allows you extend the features of an existing module by modifying its
 -- internal methods, and then revert them back to normal later if necessary.