[WINLOGON] Let the dialog manager manage the default focus (#8337)

- The single default button in the "Shutdown Computer" and "GINA failed
  to load" dialogs will be automatically focused by the dialog manager,
  so there is no need to invoke `SetFocus()` in their `WM_INITDIALOG`
  handler -- which also erroneously returned `TRUE`, thus ignoring any
  focus set by the caller :D

- Use `DeleteMenu()` instead of `RemoveMenu()` so that it'll free any
  memory resources.

base/system/winlogon/sas.c

@@ -1122,8 +1122,8 @@ ShutdownComputerWindowProc(
         }
         case WM_INITDIALOG:
         {
-            RemoveMenu(GetSystemMenu(hwndDlg, FALSE), SC_CLOSE, MF_BYCOMMAND);
-            SetFocus(GetDlgItem(hwndDlg, IDC_BTNSHTDOWNCOMPUTER));
+            /* Remove the Close menu item */
+            DeleteMenu(GetSystemMenu(hwndDlg, FALSE), SC_CLOSE, MF_BYCOMMAND);
             return TRUE;
         }
     }

base/system/winlogon/winlogon.c

@@ -431,8 +431,6 @@ GinaLoadFailedWindowProc(
                 wsprintfW(text, templateText, (LPWSTR)lParam);
                 SetDlgItemTextW(hwndDlg, IDC_GINALOADFAILED, text);
             }
-
-            SetFocus(GetDlgItem(hwndDlg, IDOK));
             return TRUE;
         }