refactor(di): drop manual PlatformUtil and LogProxy wiring (DI-3)

C3's Phase-1 bridge in Plugin.ctor already pulls IPlatformUtil and
IPluginLogProxy out of the container right after the host builds, so
the manual `new DalamudPlatformUtil()` / `new DalamudPluginLogProxy`
assignments in Phase-0 were just allocating throwaway instances that
got overwritten a few lines later.

Phase-0 helpers that run before the container build
(MigrateFromChatTwoLayout, LanguageChanged, ImGuiUtil.Initialize) do
not touch Plugin.PlatformUtil or Plugin.LogProxy, so the brief
null-window between the schema gate and the container build is safe.

The DalamudPlatformUtil and DalamudPluginLogProxy wrapper classes
themselves stay in the code; DI-4 (logger migration to ILogger<T>)
will eventually retire the proxy for new sites but EmoteCache,
AutoTranslate, MemoryUtil and WrapperUtil keep using it.

HellionChat/Plugin.cs

@@ -193,11 +193,11 @@ public sealed class Plugin : IAsyncDalamudPlugin
 
         Config = Interface.GetPluginConfig() as Configuration ?? new Configuration();
 
-        // Wire platform indirection before LoadAsync allocates anything that
-        // needs Util.* — services then read Plugin.PlatformUtil instead of
-        // hitting the Dalamud static surface directly.
-        PlatformUtil = new DalamudPlatformUtil();
-        LogProxy = new DalamudPluginLogProxy(Log);
+        // PlatformUtil and LogProxy are filled from the DI container in
+        // Phase-1 below (`_host.Services.GetRequiredService<IPlatformUtil>()`
+        // and the LogProxy equivalent). Phase-0 helpers that run before that
+        // point (MigrateFromChatTwoLayout, LanguageChanged, ImGuiUtil.Initialize)
+        // do not touch either static, so the brief null-window is safe.
 
         // Schema gate: v1.4.x requires config v16+. Users on older schemas
         // must install v1.4.2 first to run the migration chain. v17 adds