simpleperf: Remove stack and register fields for samples without
userspace stack

Otherwise, these fields will be left unrecognized.

Bug: 273341791
Test: run simpleperf_unit_test
(cherry picked from https://android-review.googlesource.com/q/commit:428d4a5fdb7745f73f52e930120dba9d2f215c26)
Merged-In: I481fa7fb21d9155349ab5c90a8ddf834dc364a08
Change-Id: I481fa7fb21d9155349ab5c90a8ddf834dc364a08
3 files changed