Move client-specific files to 'src/client' (#7902)

Update Android.mk
Remove 'src/client' from include_directories

src/script/lua_api/l_env.cpp

@@ -40,7 +40,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "face_position_cache.h"
 #include "remoteplayer.h"
 #ifndef SERVER
-#include "client.h"
+#include "client/client.h"
 #endif
 
 struct EnumString ModApiEnvMod::es_ClearObjectsMode[] =