Remove unused PROMETHEUS_RATE_DURATION

It was replaced by the QUERY environment in [1].

[1] afe631a2d0335a010f8f784b144f37305ece0147

Change-Id: I6e5780f93036c852c1de0aeef1eb68f41855838b
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
1 file changed