Remove pal_exerciser related functions from `generator.py`

Hello,

While bringing up a new target for the BSA tests, I noticed that `generator.py` still creates several non-bare metal applicable functions. I assume that at some point these have been either moved to the VAL layer or in separate files `pal_exerciser.c` for example. I notice these functions are non existent in the RDN2 target code.

Should `generator.py` be tidied up?