perf/x86: Remove unused PERF_PMU_CAP_HETEROGENEOUS_CPUS capability

Since commit bd275681

 ("perf: Rewrite core context handling") the
relationship between perf_event_context and PMUs has changed so that
the error scenario that PERF_PMU_CAP_HETEROGENEOUS_CPUS originally
silenced no longer exists.

Remove the capability to avoid confusion that it actually influences
any perf core behavior. This change should be a no-op.

Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230724134500.970496-3-james.clark@arm.com