video: Remove unused bootstrap declarations

Pandora and KMSDRM_Legacy are not used anywhere.

src/video/SDL_sysvideo.h

@@ -465,7 +465,6 @@ extern VideoBootStrap X11_bootstrap;
 extern VideoBootStrap WINDOWS_bootstrap;
 extern VideoBootStrap WINRT_bootstrap;
 extern VideoBootStrap HAIKU_bootstrap;
-extern VideoBootStrap PND_bootstrap;
 extern VideoBootStrap UIKIT_bootstrap;
 extern VideoBootStrap Android_bootstrap;
 extern VideoBootStrap PS2_bootstrap;
@@ -475,7 +474,6 @@ extern VideoBootStrap RISCOS_bootstrap;
 extern VideoBootStrap N3DS_bootstrap;
 extern VideoBootStrap RPI_bootstrap;
 extern VideoBootStrap KMSDRM_bootstrap;
-extern VideoBootStrap KMSDRM_LEGACY_bootstrap;
 extern VideoBootStrap DUMMY_bootstrap;
 extern VideoBootStrap DUMMY_evdev_bootstrap;
 extern VideoBootStrap Wayland_bootstrap;