Validator logos appear inconsistently

[michaelotis]

In this file,

https://github.com/harmony-one/staking-dashboard/blob/master/appengine/src/services/sync/validators-avatars.ts

logos are populated from both github and keybase. This creates an inconsistent loading experience where logos are not loaded. This has been brought up as an issue before and was closed with no response. While a small issue, it is a very large issue in the validator community when their logos sporadically load because they're using the recommended method of using keybase.

I propose to remove all github pointers and only use keybase and attempt to determine if the caching mechanism is flawed which is why logos aren't loaded properly.