fix(api): handle missing intermediate keys in poc index (#7029)

Sometimes, if you reset or mess with the index file, it will be valid enough to pass precondition checks but be missing the left or right intermediate keys and cause errors.

Author: sfoster1

api/src/opentrons/calibration_storage/delete.py

@@ -120,9 +120,13 @@ def _remove_pipette_offset_from_index(pipette: str, mount: Mount):
     index_path = offset_dir / 'index.json'
     blob = io.read_cal_file(str(index_path))
 
-    if pipette in blob[mount.name.lower()]:
+    try:
         blob[mount.name.lower()].remove(pipette)
         io.save_to_file(index_path, blob)
+    except (KeyError, ValueError):
+        # If the index file does not have a mount entry, you get
+        # an error here
+        pass
 
 
 def delete_pipette_offset_file(pipette: str, mount: Mount):