examples/performance-thread: remove unused hits count

examples/performance-thread: remove unused hits count

Reported by clang 13.
This patch removes the hits variable from the cpu_load_collector function
within the performance thread example app as it is an unused but set
variable.

Bugzilla ID: 881
Fixes: d48415e1fee3 ("examples/performance-thread: add l3fwd-thread app")
Cc: stable@dpdk.org
Reported-by: Liang Longfeng <longfengx.liang@intel.com>
Signed-off-by: Conor Walsh <conor.walsh@intel.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>