psa: Remove S-mode only code

Remove all PSA S-mode only code, as it is unused. Only PSA S targets
would use the code, and we've removed those targets in a previous
commit.

Ensure all tests for S-mode code we are deleting is also removed, even
if that code would run in NS-mode. Keep any tests that also test our PSA
emulation support (for single v7-M targets).

Signed-off-by: Jaeden Amero <[email protected]>

Author: Patater