systemd: use qualified path

Fix a documented anti-pattern:
https://github.com/openbmc/docs/blob/master/anti-patterns.md#use-of-usrbinenv-in-systemd-service-files

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: Ief24dc4a695bc2330243406a7457c518664964be
diff --git a/dist/phosphor-certificate-manager@.service b/dist/phosphor-certificate-manager@.service
index 8edbb4e..4d784d4 100644
--- a/dist/phosphor-certificate-manager@.service
+++ b/dist/phosphor-certificate-manager@.service
@@ -4,7 +4,7 @@
 [Service]
 Environment=UNIT=""
 EnvironmentFile=/usr/share/phosphor-certificate-manager/%I
-ExecStart=/usr/bin/env phosphor-certificate-manager --endpoint ${ENDPOINT} --path ${CERTPATH} --type ${TYPE} --unit ${UNIT}
+ExecStart=/usr/bin/phosphor-certificate-manager --endpoint ${ENDPOINT} --path ${CERTPATH} --type ${TYPE} --unit ${UNIT}
 SyslogIdentifier=phosphor-certificate-manager
 Restart=always
 UMask=0007