Use justified balances for fork choice

[terencechain]

What type of PR is this?

Bug fix

What does this PR do? Why is it needed?
The fork choice has the following incorrect assumptions:

• Uses validator balances instead of effective_balances for votes
• Uses balances from last_processed_state instead of justified_state
• Initial sync process block routine has unnecessary code for preventing decoy-bounce attack. This is not needed for initial syncing.

This PR fixed all the issues above

Which issues(s) does this PR fix?

Fixes #6260

Other notes for review
Tested run time for 24 hours on both initial syncing and regular syncing

[terencechain]

Will let this run in my set up for a day before opening up for review

[codecov]

Codecov Report

Merging #6272 into master will decrease coverage by 0.05%.
The diff coverage is 47.72%.

@@            Coverage Diff             @@
##           master    #6272      +/-   ##
==========================================
- Coverage   59.96%   59.90%   -0.06%     
==========================================
  Files         325      325              
  Lines       27583    27573      -10     
==========================================
- Hits        16539    16517      -22     
- Misses       8790     8798       +8     
- Partials     2254     2258       +4