meta-phosphor: remove ssh test keys class from default image

The phosphor-deploy-ssh-keys.bbclass was intended to be an optional
method to add additional SSH keys into a test image, but the way it
was implemented the class is always creating warnings like:

    WARNING: obmc-phosphor-image-1.0-r0 do_image: Trying to deploy SSH keys
    but input variable is empty (SSH_KEYS)

Remove the inherit in the phosphor-image.  If a user wants this feature
they can edit their `conf/local.conf` to add:

    INHERIT += "phosphor-deploy-ssh-keys"

They are likely doing something similar anyhow with the SSH_KEYS
variable (adding it to the conf/local.conf).

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id06e25ba0d22f021d81ee2cd0110d696591c1f59
diff --git a/meta-phosphor/classes/obmc-phosphor-image.bbclass b/meta-phosphor/classes/obmc-phosphor-image.bbclass
index da8c337..7a213e5 100644
--- a/meta-phosphor/classes/obmc-phosphor-image.bbclass
+++ b/meta-phosphor/classes/obmc-phosphor-image.bbclass
@@ -33,7 +33,6 @@
 
 inherit core-image
 inherit obmc-phosphor-utils
-inherit phosphor-deploy-ssh-keys
 
 FEATURE_PACKAGES_obmc-bmc-state-mgmt ?= "packagegroup-obmc-apps-bmc-state-mgmt"
 FEATURE_PACKAGES_obmc-bmcweb ?= "packagegroup-obmc-apps-bmcweb"