Remove references to old LOVE_ENABLE_module_implementation defines

As far as I know they are no longer used, as autotools was the primary (only)
user and it now switches entire modules.
I've also taken the opportunity to clean up the default list in
src/common/config.h.
Oh yeah, and this fixes linux builds not having graphics or audio backends.

--HG--
branch : minor

src/modules/audio/wrap_Audio.cpp

@@ -524,7 +524,6 @@ extern "C" int luaopen_love_audio(lua_State *L)
 {
 	Audio *instance = instance();
 
-#ifdef LOVE_ENABLE_AUDIO_OPENAL
 	if (instance == nullptr)
 	{
 		// Try OpenAL first.
@@ -539,9 +538,7 @@ extern "C" int luaopen_love_audio(lua_State *L)
 	}
 	else
 		instance->retain();
-#endif
 
-#ifdef LOVE_ENABLE_AUDIO_NULL
 	if (instance == nullptr)
 	{
 		// Fall back to nullaudio.
@@ -554,7 +551,6 @@ extern "C" int luaopen_love_audio(lua_State *L)
 			std::cout << e.what() << std::endl;
 		}
 	}
-#endif
 
 	if (instance == nullptr)
 		return luaL_error(L, "Could not open any audio module.");