Update use of select_cameras

Summary: Removed `select_cameras.py` from implicitron and updated all callsites to directly index the cameras.

Reviewed By: bottler

Differential Revision: D33187605

fbshipit-source-id: aaf5b36aef9d72db0c7e89dec519f23646f6aa05

Author: nikhilaravi

pytorch3d/renderer/cameras.py

@@ -383,7 +383,7 @@ def __getitem__(
 
         kwargs = {}
 
-        if not isinstance(index, (int, list, torch.LongTensor)):
+        if not isinstance(index, (int, list, torch.LongTensor, torch.cuda.LongTensor)):
             msg = "Invalid index type, expected int, List[int] or torch.LongTensor; got %r"
             raise ValueError(msg % type(index))