TF: remove set_tensor_by_indices_to_value
# What does this PR do?

Removes our TF `set_tensor_by_indices_to_value` function and replaces all its uses by `tf.where`. They are the same, but with a different input order -- removing it means one fewer function to test while making the code easier for TF users.
_The documentation is not available anymore as the PR was closed or merged._<|||||>@sgugger The last diff belongs to @patrickvonplaten, but because the function was moved (from [here](https://github.com/huggingface/transformers/blame/a3dbbc346763c8eaa49577a448e5b5a2da1428ed/src/transformers/generation_tf_utils.py#L1631) (link from the commit immediatly before it was moved)). Last time it was touched was 2 years ago 😅 