remove duplicate spec for CONCOURSE_GC_INTERVAL

both gc.interval and gc_interval are configuring the same env var.

gc_interval is now removed.

this is to prevent an edge case when both spec were set,
bpm-release >= 1.2.5 will fail by duplicate entry error.

Signed-off-by: Rui Yang <ruiya@vmware.com>

jobs/web/spec

@@ -1062,12 +1062,6 @@ properties:
         registry_mirror:
           host: https://registry.mirror.example.com
 
-  gc_interval:
-    env: CONCOURSE_GC_INTERVAL
-    description: |
-      The interval, in Go duration format (1m = 1 minute), on which to garbage
-      collect containers, volumes, and other internal data.
-
   gc.interval:
     env: CONCOURSE_GC_INTERVAL
     description: |

jobs/web/templates/bpm.yml.erb

@@ -511,10 +511,6 @@ processes:
     CONCOURSE_GC_VAR_SOURCE_RECYCLE_PERIOD: <%= env_flag(v).to_json %>
 <% end -%>
 
-<% if_p("gc_interval") do |v| -%>
-    CONCOURSE_GC_INTERVAL: <%= env_flag(v).to_json %>
-<% end -%>
-
 <% if_p("generic_oauth.auth_url") do |v| -%>
     CONCOURSE_OAUTH_AUTH_URL: <%= env_flag(v).to_json %>
 <% end -%>