TF: remove graph mode distinction when processing boolean options
# What does this PR do?

Removes a very old `if` branch related to boolean options, as TF graph mode can handle both branches with no issues -- it passes core tests for the models I tried.

It also unblocks @sayakpaul in the demo he's building for the TF SegFormer (#17910), which requires setting `output_hidden_states` in graph mode.
_The documentation is not available anymore as the PR was closed or merged._<|||||>LGTM! All code of this type should be removed imo - it's an artifact of TF 1.x. Modern TF code is compiled by tracing and recompiled if Python flags are changed and can handle all kinds of weird Python flow control as a result.