Fixes #31757 - Drop foreman proxy pulp plugin in foreman

In 01186b1 this was added, but it
doesn't really make sense in the Foreman scenario. Only Katello can use
it, but you need more things on the proxy which is only provided by the
foreman-proxy-content scenario.

config/foreman-answers.yaml

@@ -64,7 +64,6 @@ foreman_proxy::plugin::dynflow: false
 foreman_proxy::plugin::monitoring: false
 foreman_proxy::plugin::omaha: false
 foreman_proxy::plugin::openscap: false
-foreman_proxy::plugin::pulp: false
 foreman_proxy::plugin::remote_execution::ssh: false
 foreman_proxy::plugin::salt: false
 puppet:

config/foreman.migrations/20210129165012_drop_foreman_proxy_plugin_pulp.rb

@@ -0,0 +1 @@
+answers.delete('foreman_proxy::plugin::pulp')