Make VanillaDataManager generic (#1868)

* Make VanillaDataManager generic

* Remove removed classes from docs

* Simplify generic datamanager

* Simplify code

* Add serialization tests

docs/reference/api/data/datamanagers.rst

@@ -7,25 +7,4 @@ Base
 ----------------
 
 .. automodule:: nerfstudio.data.datamanagers.base_datamanager
-   :members:
-
-Depth Datamanager
------------------
-
-.. automodule:: nerfstudio.data.datamanagers.depth_datamanager
-   :members:
-   :show-inheritance:
-
-SDF Datamanager
-----------------
-
-.. automodule:: nerfstudio.data.datamanagers.sdf_datamanager
-   :members:
-   :show-inheritance:
-
-Semantic Datamanager
----------------------
-
-.. automodule:: nerfstudio.data.datamanagers.semantic_datamanager
-   :members:
-   :show-inheritance:
+   :members: