Remove HTTP client generic Loop parameter

I think we initially thought we might need different clients for different
parts of the system, each with a unique loop  (e.g. we thought telemetry might
need some isolation). But that never happened, so it's just needless now,
especially since the async connect uses the non-generic *Loop type directly.

src/app.zig

@@ -55,7 +55,7 @@ pub const App = struct {
             .telemetry = undefined,
             .app_dir_path = app_dir_path,
             .notification = notification,
-            .http_client = try http.Client.init(allocator, .{
+            .http_client = try http.Client.init(allocator, loop, .{
                 .max_concurrent = 3,
                 .http_proxy = config.http_proxy,
                 .proxy_type = config.proxy_type,