Remove accidentally persisted log-level data

This commit gets rid of log-level data in localStorage which in some
extreme cases could fill up the entire localStorage making the app
unusable
Followup to https://github.com/matrix-org/matrix-js-sdk/pull/1880

src/vector/localstorage-fix.ts

@@ -0,0 +1,12 @@
+/**
+ * Because we've been saving a lot of additional logger data in the localStorage for no particular reason
+ * we need to, hopefully, unbrick user's devices by geting rid of unnecessary data.
+ * */
+
+if (window.localStorage) {
+    Object.keys(window.localStorage).forEach(key => {
+        if (key.indexOf('loglevel:') === 0) {
+            window.localStorage.removeItem(key);
+        }
+    });
+}