hhvm: remove check_procs' WARNING state

Checking for an absolute == 1 number of HHVM procs isn't really a good
strategy as it comes with a lot of false positives due to HHVM processes
being spawned by MediaWiki. Remove the warning state of the check for
now, relying only on the critical threshold of < 1 processes.

Change-Id: I94f71e139828907500455ee836eea8fec1f8bf3c