[BOLT] Update obsolete test cases of llvm-bolt-binary-analysis
Drop obsolete FIXME and `f_detect_clobbered_x30_passed_to_other` test
case in `gs-pacret-autiasp.s` - checking that LR is trusted before tail
call was implemented long ago (enabled with `--scanners=pauth`).
Furthermore, this particular test case is almost identical to
`bad_direct_tailcall_not_auted` from `gs-pauth-tail-calls.s`.
Drop TODO from `gs-pacret-multi-bb.s`, as currently there are `_nocfg`
test cases in `gs-pacret-autiasp.s`.
Merge `gs-pacret-autiasp.s` and `gs-pacret-multi-bb.s` to `gs-pacret.s`,
as the tests added later place `_nocfg` and `_multi_bb` test cases
into the same file.