perf target: Remove uid from target

Gathering threads with a uid by scanning /proc is inherently racy
leading to perf_event_open failures that quit perf. All users of the
functionality now use BPF filters, so remove uid and uid_str from
target.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250604174545.2853620-10-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>