Unify "Placeholder" headers with previous commit

Only impact: removed obsolete translator comment

gnucash/gnome-utils/dialog-options.c

@@ -716,10 +716,7 @@ gnc_set_default_gain_loss_account_widget(gnc_commodity *commodity)
                 col = gnc_tree_view_add_toggle_column(GNC_TREE_VIEW(
                         book_currency_data->default_gain_loss_account_widget),
                         _("Placeholder"),
-                        /* Translators: This string has a context prefix; the
-                           translation must only contain the part after
-                           the | character. */
-                        Q_("Column letter for 'Placeholder'|P"),
+                        C_("Column header for 'Placeholder'", "P"),
                         "placeholder",
                         GNC_TREE_MODEL_ACCOUNT_COL_PLACEHOLDER,
                         GNC_TREE_VIEW_COLUMN_VISIBLE_ALWAYS,

gnucash/gnome-utils/gnc-tree-view-account.c

@@ -903,9 +903,7 @@ gnc_tree_view_account_new_with_root (Account *root, gboolean show_root)
                                             NULL);
 
     gnc_tree_view_add_toggle_column(view, _("Placeholder"),
-                                    /* Translators: This string has a context prefix; the translation
-                                        must only contain the part after the | character. */
-                                    Q_("Column letter for 'Placeholder'|P"),
+				    C_("Column header for 'Placeholder'", "P"),
                                     "placeholder",
                                     GNC_TREE_MODEL_ACCOUNT_COL_PLACEHOLDER,
                                     GNC_TREE_VIEW_COLUMN_VISIBLE_ALWAYS,