[2.x] Remove duplicate navigation item filtering

[emmadesilva]

This targets HydePHP v2.x via #1568

I realized something, do we actually want to remove duplicate items? What's really the point of that? If two pages have the same label the user might be doing something wrong, so should we try to obscure that by hiding one of them? Better to have visibility so the user can find the issue and manually hide the page they don't want,

Originally posted by @caendesilva in #1568 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1f149a4) 100.00% compared to head (bd90f93) 100.00%.

❗ Current head bd90f93 differs from pull request most recent head a3cd453. Consider uploading reports for the commit a3cd453 to get more accurate results

Additional details and impacted files

@@                        Coverage Diff                        @@
##             improved-navigation-internals     #1573   +/-   ##
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  Coverage                           100.00%   100.00%           
+ Complexity                            1763      1761    -2     
=================================================================
  Files                                  184       184           
  Lines                                 4777      4767   -10     
=================================================================
- Hits                                  4777      4767   -10     

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