delete submodules (#414)

Author: tink2123

.gitmodules

@@ -4,12 +4,6 @@
 [submodule "external/book"]
 	path = external/book
 	url = https://github.com/PaddlePaddle/book
-[submodule "external/Anakin"]
-	path = external/Anakin
-	url = https://github.com/PaddlePaddle/Anakin
-[submodule "external/paddle-mobile"]
-	path = external/paddle-mobile
-	url = https://github.com/PaddlePaddle/paddle-mobile
 [submodule "external/models"]
 	path = external/models
 	url = https://github.com/PaddlePaddle/models