ConcurrentHashMap implements `containsKey` with `get`. By removing a
redundant call to `containsKey`, we guarantee better performance in our
counter services.

The geek inside measured this with JMH, and found under 4 threads of
contention, throughput on this check was 40% higher in success case.

Benchmark                                  Mode  Cnt     Score     Error   Units
TestBenchmarks.containsKeyAndGet_success  thrpt   30   432.389 ±  20.616  ops/us
TestBenchmarks.get_success                thrpt   30   606.789 ±  10.848  ops/us

Closes gh-6379