Greatly simplify history management code (#2230)

Fixes #2220

This drops the ability to shift+click on “Back” to get back to a pinned
column, but that was inconsistent, broken, and undocumented.

This also brings us slightly closer to upstream.

app/javascript/flavours/glitch/components/permalink.jsx

@@ -24,9 +24,7 @@ export default class Permalink extends React.PureComponent {
 
       if (this.context.router) {
         e.preventDefault();
-        let state = { ...this.context.router.history.location.state };
-        state.mastodonBackSteps = (state.mastodonBackSteps || 0) + 1;
-        this.context.router.history.push(this.props.to, state);
+        this.context.router.history.push(this.props.to);
       }
     }
   };