Sensu: Remove ceph and process-checks plugins from client

The sensu image became unbuildable, failing to install the ceph plugin:

    Unable to resolve dependencies: sensu-plugins-ceph requires english (= 0.6.3)

This has happened because the author of the 'english' gem has seen fit
to publish a new 0.7.0 release, and 'yank' [1] all previous releases
from rubygems.

This change removes the ceph and process-checks plugins, which both
suffer from a dependency on the yanked english 0.6.3.

[1] https://rubygems.org/gems/english/versions/0.6.3

Change-Id: I9d34413fa10b5a2920aca60b08141bfaddcc7415
Closes-Bug: #1871600
(cherry picked from commit 818dc4d6ff12a3119be072e0c68e2d2c8da9b799)

docker/sensu/sensu-client/Dockerfile.j2

@@ -57,7 +57,6 @@ RUN echo '{{ image_name }} not yet available for {{ base_distro }}' \
 # Let's cap them to the known major version that works with the ruby shipped on
 # rhel/centos (currently 2.0)
 {% set sensu_plugins = [
-    'ceph:"~>1"',
     'cpu-checks:"~>1"',
     'disk-checks:"~>2"',
     'dns:"~>1"',
@@ -75,7 +74,6 @@ RUN echo '{{ image_name }} not yet available for {{ base_distro }}' \
     'network-checks:"~>2"',
     'ntp:"~>1"',
     'openstack:"~>1"',
-    'process-checks:"~>2"',
     'rabbitmq:"~>3"',
     'redis:"~>2"',
     'uptime-checks:"~>1"',