Remove unnecessary `tcx` parameter to `param_env_to_generics`

[jyn514]

You can get a tcx from self.cx.tcx, there's no need to pass it separately.

Note that this will conflict with #82020 so you may want to wait a day or two (or not, if you don't mind rebasing).

[nipunG314]

@rustbot claim

[camelid]

I think there are also a couple of other functions that unnecessarily take tcx in the same area of the code.