Clean up unused navigation code for localStorage

[ryankeairns]

TL;DR - I believe some (all?) of the code in this commit is unused and can be removed: b1305c6

When the new nav drawer was introduced in Kibana 7.0, code was put into place in the event we wanted to handle locking the nav drawer open in the future. The future has arrived and the nav drawer can now be locked open, but new code was written to handle localStoarge of the locked state (#43916 (comment)) thus making the aforementioned commit likely obsolete.

[thompsongl]

Yes, I didn't realize that any of that code (b1305c6) was relevant when I implemented the new lockable nav. So if it has no purpose beyond nav locking, all that code is obsolete now.

[ryankeairns]

Removed by commit 4deea08