Remove redundant placeholders in forms

Using placeholders having similar (or identical) text as already present
as a label has a few issues.

First, it's a distraction. Reading the same information twice is
useless, requires an extra effort, and might even frustrate users.

Second, if users start typing before reading the placeholder and see it
disappear, they might think they're missing relevant information,
delete what they typed, and read the placeholder. That will get them
nowhere.

Finally, we display placeholders using a text offering very low contrast
against the background, so users don't think the placeholder is an
actual value entered in the field. Using such low contrast makes the
text hard to read, particularly for users with visual impairments.

So we're removing these placeholders.

This commit only deals with placeholder texts with similar (or
identical) texts as the label text. There might be other places where we
should replace placeholder texts with labels, but that's a different
topic.

config/locales/es/general.yml

@@ -5,10 +5,7 @@ es:
       erase_account_link: Darme de baja
       finish_verification: Finalizar verificación
       notifications: Notificaciones
-      organization_name_label: Nombre de la organización
-      organization_responsible_name_placeholder: Representante de la asociación/colectivo
       personal: Datos personales
-      phone_number_label: Teléfono
       public_interests_my_title_list: Etiquetas de los elementos que sigues
       public_interests_user_title_list: Etiquetas de los elementos que sigue este usuario
       save_changes_submit: Guardar cambios
@@ -22,7 +19,6 @@ es:
       user_permission_verify: Para poder realizar todas las acciones, verifica tu cuenta.
       user_permission_verify_info: "* Sólo usuarios empadronados."
       user_permission_votes: Participar en las votaciones finales*
-      username_label: Nombre de usuario
       verified_account: Cuenta verificada
       verify_my_account: Verificar mi cuenta
   application:
@@ -93,7 +89,6 @@ es:
         submit_button: Guardar cambios
       show_link: Ver debate
     form:
-      debate_title: Título del debate
       tags_instructions: Etiqueta este debate.
       tags_placeholder: "Escribe las etiquetas que desees separadas por coma (',')"
     index:
@@ -958,7 +953,6 @@ es:
       note: Añade los enlaces que sean de interés.
       add_new_link: Añadir nuevo enlace
     link_fields:
-      label_placeholder: Título del enlace
       url_placeholder: Dirección del enlace
   communities:
     show: