Multiple keys with the same name in rlds leads to the second overwriting the first one.

[yblei]

Describe the bug
Some datasets such as droid define the same key twice (i.e. gripper_position as an action as well as a proprioception).
This leads to the entry of the second key overwriting the first without further warning.

To Reproduce
Steps to reproduce the behavior:

1. import the droid dataset
2. try to access both keys after import
3. you will see, that there is only one left with the values of the key, appearing last (in this case proprioception/gripper_position)

Expected behavior
Both keys should be represented

Suggestion
We patched this problem temporarily, however we should find a long term solution.
See: yblei@06ede76