Remove duplicated keys

In the images.yml file we have a duplicate key with the same translation,
so we can remove it.

In the admin.yml file we have a duplicate key with different translation.

This translation is only used in 2 places in the application:
- In the administration table for collaborative legislation proposal index.
- In the <% provide :title do %> of the same page.

Although it is true that now the second translation (Title) is applied in
both cases, I think it makes more sense to use the first one (Proposals)
in the page title because it seems to make more sense and be more useful
to use "Proposals" instead of “Title”.

In order not to modify the behavior in the translation shown in the
administration table, we add human_attribute_name to obtain the expected
result.

app/views/admin/legislation/proposals/_proposals.html.erb

@@ -7,7 +7,7 @@
     <thead>
       <tr>
         <th class="text-center"><%= t("admin.legislation.proposals.index.id") %></th>
-        <th><%= t("admin.legislation.proposals.index.title") %></th>
+        <th><%= Legislation::Proposal.human_attribute_name(:title) %></th>
         <th class="text-center"><%= t("admin.legislation.proposals.index.supports") %></th>
         <th><%= t("admin.proposals.index.selected") %></th>
       </tr>

config/locales/en/admin.yml

@@ -619,7 +619,6 @@ en:
           title: Proposals
           back: Back
           id: Id
-          title: Title
           supports: Total supports
         form:
           custom_categories: Categories

config/locales/en/images.yml

@@ -7,7 +7,6 @@ en:
       delete_button: Remove image
       note: "You can upload one image of following content types: %{accepted_content_types}, up to %{max_file_size} MB."
       add_new_image: Add image
-      title_placeholder: Add a descriptive title for the image
     actions:
       destroy:
         notice: Image was deleted successfully.