Minor updates to adjoint notebook removing to_simulation() calls where possible

[yaugenst-flex]

Updates a few notebooks to remove JaxSimulation.to_simulation() calls where safe to do so, particularly before to_gds() calls as this is fixed as of flexcompute/tidy3d#1660.
The changes are very conservative, I did not remove to_simulation() calls if the resulting simulation object is being reused for other things, such as running a simulation.

[tylerflex]

Looks good, thanks for taking care of this! (there might be a few other instances, eg in the mode converter but it's ok, we can just clean them up when we notice them)