Host: Remove unnecessary function

Remove Host_UpdateMainFrame(). The only non-empty call happened in
DolphinNoGUI which called s_update_main_frame_event.Set(), but
DolphinNoGUI never waits on that event.

Source/Core/Core/Core.cpp

@@ -242,8 +242,6 @@ bool Init(Core::System& system, std::unique_ptr<BootParameters> boot, const Wind
   INFO_LOG_FMT(BOOT, "Starting core = {} mode", system.IsWii() ? "Wii" : "GameCube");
   INFO_LOG_FMT(BOOT, "CPU Thread separate = {}", system.IsDualCoreMode() ? "Yes" : "No");
 
-  Host_UpdateMainFrame();  // Disable any menus or buttons at boot
-
   // Manually reactivate the video backend in case a GameINI overrides the video backend setting.
   VideoBackendBase::PopulateBackendInfo(wsi);
 
@@ -342,7 +340,6 @@ static void CPUSetInitialExecutionState(bool force_paused = false)
     bool paused = SConfig::GetInstance().bBootToPause || force_paused;
     SetState(system, paused ? State::Paused : State::Running, true, true);
     Host_UpdateDisasmDialog();
-    Host_UpdateMainFrame();
     Host_Message(HostMessageID::WMUserCreate);
   });
 }

Source/Core/Core/FifoPlayer/FifoPlayer.cpp

@@ -262,7 +262,6 @@ public:
 
       case CPU::State::Stepping:
         cpu.Break();
-        Host_UpdateMainFrame();
         break;
 
       case CPU::State::Running:

Source/Core/Core/Host.h

@@ -63,7 +63,6 @@ void Host_RequestRenderWindowSize(int width, int height);
 void Host_UpdateDisasmDialog();
 void Host_JitCacheInvalidation();
 void Host_JitProfileDataWiped();
-void Host_UpdateMainFrame();
 void Host_UpdateTitle(const std::string& title);
 void Host_YieldToUI();
 void Host_TitleChanged();

Source/Core/Core/State.cpp

@@ -456,8 +456,6 @@ static void CompressAndDumpState(Core::System& system, CompressAndDumpState_args
       Core::DisplayMessage(fmt::format("Saved State to {}", temp_path.filename().string()), 2000);
     }
   }
-
-  Host_UpdateMainFrame();
 }
 
 void SaveAs(Core::System& system, const std::string& filename, bool wait)