Avoid using localStorage for reload interval

[c-bata]

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Reference Issues/PRs

For #719

What does this implement/fix? Explain your changes.

Avoid using localStorage for reload interval to simplify the behavior. Moreover, I removed the code for graph visibility which is actually unused.

[c-bata]

@nabenabe0928 Could you review this PR?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6150418) 69.48% compared to head (ce5fe78) 69.48%.
Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #761   +/-   ##
=======================================
  Coverage   69.48%   69.48%           
=======================================
  Files          35       35           
  Lines        2353     2353           
=======================================
  Hits         1635     1635           
  Misses        718      718           

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[nabenabe0928]

LGTM!