[common] Refactor Protected Files slightly

This commit refactors PF code without changing functionality:
- Many renames of data structs, variable names, func names
- More readable comments (and fixing incorrect comments)
- Removed unused `pf_get_handle()`
- Removed unused `g_pf_mrenclave_key`, `g_pf_wrap_key`, etc.
- Removed all mentions of `list`/`LIST` operations (were unused)

This commit contains changes (renames) in `pf_tamper.c`, but this file
and corresponding tool are not tested and most probably broken. We did
the changes purely to survive compilation.

Signed-off-by: Dmitrii Kuvaiskii <[email protected]>