lua: remove a ton of unneeded parentheses

For whatever reason, some of the lua code (particularly the osc and
ytdl_hook) is full of a bunch of stuff like if (foo), if not (foo ==
nil), etc. The parenthesis aren't needed in lua and actually just look
weird since nobody actually writes lua like this. You can see most of
the other conditionals are written normally. So cleanup the style to
match when the parenthesis clearly aren't doing anything. Not directly
related, but also add some spaces on a few math operations while we're
at it.

player/lua/stats.lua

@@ -1092,7 +1092,7 @@ local function cache_stats()
     append(stats, opt_time(a) .. " - " .. opt_time(b), {prefix = "Packet queue:"})
 
     local r = nil
-    if (a ~= nil) and (b ~= nil) then
+    if a ~= nil and b ~= nil then
         r = b - a
     end
 
@@ -1174,7 +1174,7 @@ local function record_cache_stats()
 
     local a = info["reader-pts"]
     local b = info["cache-end"]
-    if (a ~= nil) and (b ~= nil) then
+    if a ~= nil and b ~= nil then
         graph_add_value(cache_ahead_buf, b - a)
     end
 
@@ -1274,7 +1274,7 @@ local function unbind_scroll()
     end
 end
 local function update_scroll_bindings(k)
-    if (pages[k].scroll) then
+    if pages[k].scroll then
         bind_scroll()
     else
         unbind_scroll()