Delete loot-dialog element

It's more effort to maintain than just using the paper-dialog element
directly.

src/gui/html/elements/loot-dialog.html

@@ -1,56 +0,0 @@
-<!--
-<loot-dialog> is an extension of <paper-dialog> that gives it a <dialog>-like API.
-
-Still missing compared to <dialog> are:
-
-1. No `close` or `cancel` events.
-2. No ::backdrop pseudo-element.
-3. No `form[method="dialog"]`.
--->
-
-<link rel="import" href="../../../../bower_components/polymer/polymer.html">
-<link rel="import" href="../../../../bower_components/paper-dialog/paper-action-dialog.html">
-
-<polymer-element name="loot-dialog" extends="paper-action-dialog" transition="core-transition-center" layered="false">
-    <template>
-    <style>
-    :host {
-        margin: 24px 40px;
-    }
-    :host::shadow #actions {
-        padding: 16px 16px 8px;
-        /* This is and the div CSS would be better done by moving the div before
-           both content elements, this is a hack to do the same without editing
-           the HTML. */
-        justify-content: flex-end;
-    }
-    :host::shadow #actions > div {
-        flex: none;
-    }
-    :host::shadow h1 {
-        font-weight: 500;
-        font-size: 1.429rem;
-    }
-    </style>
-    <shadow></shadow>
-    </template>
-    <script>
-    Polymer({
-        show: function() {
-            this.backdrop = false;
-            this.autoCloseDisabled = false;
-            this.setAttribute(opened, true);
-        },
-        showModal: function() {
-            this.backdrop = true;
-            this.autoCloseDisabled = true;
-            this.open();
-            this.setAttribute('opened', true);
-        },
-        close: function(retVal) {
-            this.setAttribute('returnValue', retVal);
-            this.super();
-        },
-    });
-    </script>
-</polymer-element>