Remove tensorflow and tf_models as submodules now that they're linked as bazel rules.

Author: kirilg

.gitmodules

@@ -1,6 +0,0 @@
-[submodule "tensorflow"]
-	path = tensorflow
-	url = https://github.com/tensorflow/tensorflow.git
-[submodule "tf_models"]
-	path = tf_models
-	url = https://github.com/tensorflow/models.git