fix: httproute status.parents is not cleaned up

[Xunzhuo]

What type of PR is this?

What this PR does / why we need it:

The fix ensures that the status.parents field accurately reflects the current state of the spec.parentRefs field.

Which issue(s) this PR fixes:

Fixes #5581

Release Notes: Yes/No

[codecov]

Codecov Report

Attention: Patch coverage is 82.85714% with 6 lines in your changes missing coverage. Please review.

Project coverage is 65.20%. Comparing base (e374db4) to head (a310cd0).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/provider/kubernetes/status.go	82.85%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5679      +/-   ##
==========================================
- Coverage   65.20%   65.20%   -0.01%     
==========================================
  Files         213      213              
  Lines       34108    34140      +32     
==========================================
+ Hits        22241    22261      +20     
- Misses      10521    10530       +9     
- Partials     1346     1349       +3     

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